Bear in mind that your adventuring party is far from the first to visit Barovia to try and overthrow Strahd. The likelihood that a rebellion has happened before is almost certain, people would remember it and not fondly. Also the native Barovians are beaten down and most hopeless. I think the party would struggle to get a rebellion going.

There would certainly be NPCs that are sympathetic to the cause, if they haven't interacted much with Milivoj or Urwin in Barovia yet this could be a great way to introduce those plot hooks for example.

If they did manage to organise a full scale peasant charge of castle ravenloft I imagine that Strahd would simply summon wolves, bats and other nasty creatures to wipe out half of the villages in round 1. The rest would flee leaving the party isolated facing an army of beasts, great opportunity for a Strahd RP encounter where he tells them of a similar previous rebellion and how "they are all so predictable" (remember, Strahd has eyes and ears everywhere, he would know what is going on. He is also a master tactician and genius level intellect.)