Yeah, he overestimated himself. But there were still a wide support for him, from the Russian public and inside the establishment. He should've bet on continuing until at least it got more intense and closer to Moscow (without turning into a full blown battlefield). Then set ultimatums for Putin to appease his demands and then back off with maximum achievements of his objectives.
After all, he barely faced any armed forces from their location in Ukraine until arriving at the the borders and onwards, proving that he had an 'upper-hand' to a certain extent with support of the Russian army stationed there or other 'docile' soldiers who may not like him, but still not willing to fight him either.
The Russian army was also not prepared. Wagner even shot down four helicopters inside Russia as they pushed forward. Overall, while Wagners capabilities did not match their counterparts, their best chance was getting more military fractions to defect along their advancements. Even inside Moscow, I'm sure he had insiders and people with allegiance towards him inside the army, intelligence and the gov't.
If his did as I suggested, it would've ended with some form agreement anyways irrespective of the aftermath, like now but with better outcome for him/Wagner. I guess, he wasn't bold enough to continue