A lot, certainly but a big chunk of that would have to go on transfer fees and higher wages to bring in better quality players, just so they could get anywhere near a level where they'd be able to compete.but think how much money they would make from one season in the Premiership.
If they went straight back down they'd still be lumbered with the high wage bill, with no guarantee of going back up. The alternative is to sell the high earners for what they can get and replace them with cheaper players, but then of course the squad is going to be lacking quality. Either way, it's not a good position to be in.
Clubs like Nottingham Forest, Bradford City and Leeds United have all had spells in the Premier League in recent years and sank dramatically following their relegation from the top flight the latter two (and Leeds in particular) suffering severe financial troubles due to them gambling everything on the hope that they could maintain (and then regain) their Premier League status.
Those who are promoted to the top flight, tread carefully.