It's very strange how things are going right now. The fact that they are quite effortlessly moving hundreds of kilometers through Russian territory is quite telling.
They already control a city with one million inhabitants, with one of the five military headquarters of the Russian military. I wouldn't call this a "small rebellion" yet.
If they would merely keep Rostov, a city with one million citizens, this would already be an enormous problem for Russia. But the Wagner group is going all-out, and I strongly doubt whether they'll be able to oust the Russian government.