I noticed that with the Imperator Invictus mod slave revolts have made a comeback (see my post initial here
https://forum.paradoxplaza.com/forum/threads/mod-imperator-invictus.1473328/page-12#post-27684639 ).
I can't say whether their mechanic is unmodified or not, mainly because it has been a while that they happened in the unmodified game - and back then IR was a different game (e.g. old army system without levies). It was never a problem to instantly crack down the revolts and all you had to decide was how to punish the slaves (affecting how many you would g o back and how long you are saves from more uprisings)
However, my experience with the I.I.-mod is different now (though again this is not necessarily caused by the mod...) - the first couple of revolts "ended" by the slaves quickly wandering abroad. And no trace of them was seen again - which solved the revolt, but also means all slaves being lost.
After extending my empire one day such a revolt happened far away from the core of my empire and my levies were still on their way, when the slaves crossed the border as usual. But this time something strange happened - they somehow managed to get behind my back quickly (I'm unsure if they took a clever route or if some weird teleporting stuff was going on) - and the first time ever in IR I got my governor cruzified by slaves, followed by this guy becoming my personal Spartacus:
My "problem" is now that this character has vanished with the slave army again by crossing the border - and I have no means to find out whether (and if, where) he is still active with his army. I tracked him down with the character search and pinned him in the ledger, but that doesn't help me to judge whether he is still an on-map threat (and the decision, if and when to disband my levies):
A bit of an irony is the "Prime Heir" state he has...
So my question goes out to anyone who has experience (be it with older vanilla IR or I.I. mod) with a slave revolt passing the point where they get a leader - do they roam the map forever, until randomly invading you again? Do other nations engange them or have they some kind of immunity?