This is a bit trivia-seeking, as there are countless situations where monarchs or even states have been excommunicated without significant lasting consequences. Indeed, you could argue that the vast majority of excommunications were entirely political in nature and more often than not had very little consequence, seeing as whomever had been excommunicated was almost always already in open conflict with the church to begin with.

In 1318, for example, Pope John XXII, angry at the Lord of Milan, Matteo Visconti (for... many reasons) got the bishops of Asti and Como (two cities in the Visconti domain) to accuse Matteo of heresy (specifically, necromancy). Pope John couldn't get the Bishop of Milan on board though (the bishop was Matteo's youngest son, Giovanni) but once the official accusation was processed John XXII nonetheless took the liberty of extending it to two allies of Matteo's: Cangrande della Scala, Lord of Verona, and Passerino Bonacolsi, Lord Of Mantua. The trial took place in 1320 in Avignon, but Matteo did not participate, citing his old age. Although Matteo could count on his successors and allies to fight the guilty verdict, he was excommunicated nonetheless. The excommunication was a desperate attempt to counteract the increasingly powerful Viscontean state in Lombardy, but overall did not have much of an impact on Matteo's final years as ruler, nor did it stop him from retiring to a monastery (however, his son was forced to bury his father in an unmarked grave, lest his enemies exhume his remains and burn them as a heretic). Although Lombardy at the time was turbulent, the Papal-backed Torriani dynasty would have challenged the Visconti's rule even without Matteo's excommunication.

Another example is the Republic of Venice, which was excommunicated multiple times in its history. Notably, in 1606 the entire Republic was placed under an interdict (a sort of collective excommunication) but the news was met with indifference from the cosmopolitan and mostly secular citizenry as well as its free-minded clergy (who had caused the interdict in the first place). Norwich recounts the incident rather colorfully in his History of Venice.

That's not to say an excommunication wasn't ever a big deal; it was certainly a delegitimizing pain-in-the-butt to deal with, and the Papacy was handing them out as late as 1949, when a Papal Bull declared that Communists were excommunicated. But, like Matteo Visconti and the citizens of the Republic of Venice, the Communists already knew they weren't much liked by the Pope.