Breakaway states in general, fair enough... but not when it's a group of mercenaries which can also be classified as terrorists that went from 8k members to +50k over the last year, including recruiting quite a sum of people from prisons.
Definitely, a PMC gaining control of a state is always, in general, a
really bad idea. If Wagner Group does end up forming a breakaway state, then in hindsight, the US trading away one of the biggest arms dealers in the world for Britney Griner is going to have even more far-reaching consequences.
A heavily militant state in Eastern Europe who will sell their services to the highest bidder, be it terrorism or covert operations, is catastrophically terrifying in the 21st century.