Yeah, they are fucked.
Sporting sanction wise though, isn't just the EPL? So the worst they can do is enforce a points deduction / demotion, possibly strip them of all titles, and potentially a transfer ban?
The reason they are fucked is because every man and his dog is going to sue the living daylights out of them, they will win, and man city will have to cover those costs out of the SCR regulations. We're talking hundreds of millions... several hundreds of millions.
Miss out on champions league footy... you can sue. Miss out on europea league... you can sue... Knocked out the FA cup semi final... you can sue... Stoke and Watford have both just won an FA cup and are due compensation for missing out on europe...
Any European side that they knocked out during the period when they breached Uefa FFP rules... you would imagine they may also have a case...
They have also financially doped their squad through illegal hidden payments and raised the cost of all teams in the premier league (and wide football league) over the period of a decade (give or take)...
Goes on and on.
Saints can make a claim that they damaged our champions league chances (we finished 3 points behind them in 4th)... equally they've poached youth academy starlets off of us through inflated wages and raised the cost of competing in the premier league.
On the most simple level. Every single club in the league will be able to claim along the lines that they have missed out on one position's worth of prize money for each season where city broke the spending rules...