All religious ideals aside, if Jesus had been a real man who lived during the Roman occupation of Canaan (I couldn't find an exact name for the nation in those days) and he did in fact spread idealistic, religious notions superseding Roman right of rule over the Jews, what would the possible consequences have been if the Pharisees hadn't crucified him and the Romans had had enough? If his message had gained enough traction and he hadn't been killed, is it possible there may have been a massive genocide campaign against the Jewish people?
Not to invite any controversy or give offense, but if the Romans were known for wiping out entire peoples for dissent against Roman rule, then is it reasonable to assume that by crucifying Jesus the Pharisees actually saved millions of lives?
To begin with, the consensus among historians is that Jesus did exist as a real man in Roman Judaea (as it was called at the time), as you can read about in the FAQ, as well as this answer by u/brojangles which details what evidence we have for him, and this recent discussion by u/koine_lingua and others might also be relevant.
When it comes to your main question, it is unlikely that there would be a genocide against the entire Jewish people in that case. As I myself wrote about in this thread, we know about several other preachers who claimed prophethood in the same period, and their career tended to end with their execution and the violent suppression of their followers by Roman troops, but generally not with mass murder against uninvolved Jews
if the Pharisees hadn't crucified him
The pharisees did not crucify Jesus. The claim that the pharisees or any other group of Jews were responsible for the death of Jesus is literally the oldest antisemitic libel there is. Please do not repeat it.
One of the earliest and clearest examples appears in Matthew 27:25, written several decades after the events. When Pontius Pilate second-guesses his decision to have Jesus crucified, Jews are caricatured as a bloodthirsty lynch mob.3 This narrative is patently false. While certain leaders in the local Jewish community felt that Jesus’ teachings were politically subversive, experts have gathered that Jesus was not perceived as particularly threatening or enraging to the Jews around him.
Jesus was a Jew living under Roman military occupation who was sentenced to death by the Roman military governor using a Roman method of execution for crimes against Rome. The Jewish leadership at the time (who were Sadducees, not pharisees, by the way) had been stripped of the power to try people for capital crimes and had little to no influence over the occupying Roman government. Moreover, the many surviving records of the pharisees show that they were largely against capital punishment.
A Sanhedrin that executes a transgressor once in seven years is characterized as a destructive tribunal. Since the Sanhedrin would subject the testimony to exacting scrutiny, it was extremely rare for a defendant to be executed. Rabbi Elazar ben Azarya says: This categorization applies to a Sanhedrin that executes a transgressor once in seventy years. Rabbi Tarfon and Rabbi Akiva say: If we had been members of the Sanhedrin, we would have conducted trials in a manner whereby no person would have ever been executed.