This question has come up before, but I'm not going to link my older answer because I think more can and should be said, in different words.

The Wikipedia article on the Samnites has some...issues. An earlier revision of the page, for example, did not actually know the difference between the Samnites and Sabines, and used the two words interchangeably, including in the sentence on Sulla's "ethnic cleansing campaign," as Wikipedia puts it. It also, among other things, conveniently leaves out the Lucanians, who also persisted in their resistance at the end of the Social War.

Strabo 5.4.11, which the Wikipedia article cites, gives some interesting information. Strabo says that when Sulla fought the Samnites and Lucanians under the walls of Rome he butchered his prisoners--Plutarch gives the same information. Strabo also says that when Sulla drew up the proscription lists he did not stop ἢ πάντας τοὺς ἐν ὀνόματι Σαυνιτῶν διέφθειρεν ἢ ἐκ τῆς Ἰταλίας ἐξέβαλε, "until he had killed or driven from Italian all those who were in the name of Samnites." The unidiomatic translation is deliberate: Strabo's phrasing, while understandable in Greek, is unusual and very elliptical. Strabo further states that the towns of the Samnites had shrunk in his time to be little more than villages.

What is Strabo actually describing? The slaughter of Samnite prisoners seems easy enough to explain, and can be overlooked as an indicator of a "campaign of ethnic cleansing." Sulla was, after all, famous among later authors for his indiscriminate massacres. The bit about the proscriptions is hard to understand. For Strabo's statement to be literally true Sulla must have included in the proscription lists more Samnites than the total number of the proscribed. That is clearly impossible. The proscriptions targeted senators and equites, not the population in general. It may be that Strabo with the strange phrase ἐν ὀνόματι Σαυνιτῶν might be using ὀνόματι in its meaning of "famous," which would then limit this statement to all the notable Samnites, i.e. the Samnite aristocracy. I'd have to do a lot of digging through the TLG to see if this very attractive reading is paralleled elsewhere, though. Still, clearly Strabo must be talking about Samnite nobles, not the Samnite population in general. On its surface the statement is patently impossible, and is out of character for the proscriptions.

Moreover, Strabo's belief that the Samnite name, even if restricted only to the nobility, had been driven to extinction was not even true in his own time, a few decades later. Samnite names continue to be found in the nobility in the decades after Sulla's death, and under Augustus especially increasingly appear in the senate. This is pertinent to Strabo's comment on the condition of Samnite towns. The precise date of Strabo's publication is uncertain, but it's an Augustan text for sure. Within Strabo's own lifetime Augustus launched a very successful urbanization campaign in Samnite country. Samnite settlements had always been primarily rural, and Augustus' program was the first serious urbanization in the region. Strabo himself acknowledges that there are exceptions to his statement about Samnite towns. He says that Βενεουεντὸν δ᾽ ὅμως συνέστηκεν εὖ καὶ Ὀυενουσία, "But nevertheless Beneventum has managed well, as has Venusia." Venusia had revolted against Rome during the Social War and was refounded as a colony by the Triumvirs in 43, but Beneventum had not--in fact, in 89 the town was made a full municipium. The city had had a large Latin influence (and likely a large Roman population as well) since 268 when it was designated a colony under ius Latinum (so not a "full" colony), but we find plenty of traces of Samnites (their names are all over local inscriptions) until fairly late, and clearly the city was still "Samnite" enough for Strabo to consider it a Samnite town.

The evidence, then, does not actually show that the Samnites "disappeared from history," to use Wikipedia's phrase. The evidence for Sulla's actions against the Samnites is somewhat unclear, but does not seem to show clearly any kind of "campaign" of extermination. Still, can we call this an act of "ethnic cleansing?" Our evidence, it seems to me, is far too incomplete, even before we consider what we mean by "ethnic cleansing" and the relevance of that precise phrase to the ancient world. Some scholars do consider Sulla's actions against the Samnites to be deliberately genocidal. Harriet Flower, for instance. Later authors certainly considered the brutality with which Sulla treated the Samnites to be abhorrent, although these actions are (pretty much everywhere outside of Strabo, where the context is different) included as examples of the general cruelty that Sulla was said to have unleashed. Excepting Strabo's comments on the proscriptions, which are hard to interpret in any case, what we're actually told happened does not seem to greatly different than any number of Roman acts of conquest throughout countless provinces. Roman armies and commanders routinely crushed the ability of peoples who resisted to continue their opposition. We do not see any policy of ethnic destruction laid out for us in any of the authors that deal with imperialism, but the ethnic nature of ancient settlement means that such actions often were, of a necessity, ethnic in nature. The capture of a city, the conquest of a people, the subjugation of rebels in a province were all brutal acts by their very definition, and when restricted by location almost always take an ethnic character to the observer looking back. Are these examples of "ethnic cleansing?" I don't know, but if they are then I think we need to take a step back and evaluate how all state violence lines up with regards to such a definition.

In another vein, the use of the term "ethnic cleansing" invites certain responses that I'm not sure are appropriate, especially in certain contexts of delivery. It's one thing for Harriet Flower to describe Sulla's actions as "ethnic cleansing" (more or less as an aside, though) in her peer-reviewed, academically-published book that was intended for and will likely only ever be read by people who have devoted a lot of time and energy thinking, at an academic level, about the boundaries of the term. It's quite another to drop it on the internet or on reddit for flyby readers to stumble on. Whenever we speak of genocide or ethnic cleansing in such contexts we invite the revolting specter of "genocide Olympics," which all too frequently leads to the "disqualification" of various tragedies by the argument that this-or-that genocide was worse. That's dodging the point, and I don't think it serves very much use to argue over whether we should label Sulla's activities as "ethnic cleansing" or not. We know what the evidence tells us: Sulla massacred several thousand Samnite and Lucanian prisoners, and included some number of Samnites in his proscriptions. He did not, Plutarch tells us, actually lead a campaign into Samnium, but ended his pursuit of the defeated Samnites at Antemnae, a Latin city. Strabo claims that Sulla said that ὡς οὐδέποτ᾽ ἂν εἰρήνην ἀγάγοι Ῥωμαίων οὐδὲ εἷς, ἕως ἂν συμμένωσι καθ᾽ ἑαυτοὺς Σαυνῖται, "that no one of the Romans could live in peace so long as the Samnites remained against them." Hamilton and Falconer's translation, which is probably what Wikipedia is using, translates that as "so long as any of the Samnites survived," which would be quite an unusually strong statement for a Roman commander, who might more typically have sought to destroy the ability of a hostile people to continue their opposition. But the text doesn't actually say that, and if Strabo is right Sulla described the Samnites as an existential threat so long as they remained in a united body opposed to the Romans, which seems more characteristic of the Roman imperial mindset. Whether Sulla intended the annihilation of the Samnite people (for which I do not think there is much evidence) he conspicuously failed: Samnium was alive and well a few decades later, and Samnite names graced the expanded Augustan senate whose new organization traced back to Sulla. Whatever happened was a tragedy and a brutality against the Samnite people: the execution of prisoners alone would have been considered even in antiquity horrific, and for this reason our sources include it. We should not allow labels, or the lack thereof, to distract us from the reality that ancient warfare, and perhaps especially civil war, was characteristically brutal.