I doubt he'd get anything close to that. Rather than bite a financial bullet like that the Ferguson PD could easily cook up some procedural mistake Wilson made during the Brown shooting and dismiss him for cause. He'll remain on the force until it's clear he's off the hook in terms of any changes and then he'll resign.
The problem with that is the impact it has on all the other officers in Ferguson, plus any officer or candidate who may want to come work in Ferguson.
It’s in the Ferguson PD’s interest to be generous. Very generous. It may be the only thing that keeps their department from imploding.