Most of the time,a rich businessman takes over and wipes out most of the debt but that does not happen till 3-4 years usually
The debt isn't a problem in the future. In my Man U saves I still get massive transfer money to spend with a big wage budget as well. Only when the AI manage Utd do they seem to decline.
For takeovers, sometimes its a board member or once in a while you can get a tycoon taking over.
In my game, they went into administration, sold the best players and ended up in league one after about twenty years.