Somebody will take them over - in time where they can buy as low as possible. Just on the precipice of falling out of top flight footy would probably be the time all buyers come crawling out of the woodwork. The debt is what is putting buyers off. I mean no offense but the most recent sale of a top flight team (Liverpool) also had crippling debts but still rated as worth around a billion by Forbes but it sold for a total including wiping the debts for around 1/2 that valuation. Everton has nowhere near the revenue raising capabilities (despite being crippled with debt Liverpool still generated aprrox 200mil euros p/a over the last 5 or so years). The last Forbes valution I can find says around 200mil for Everton, with the current economy realistically I suppose from anywhere from 1/4 to 1/2 of that valuation will be the sale price. If a Shiekh type buyer comes in it's actually not too bad value. 50-100 mil + debts gets you a well established epl team with a good manager, a squad at its peak, needing only 2-3 players to compete for Europe with their own ground.
I'm going off the valuations in these articles from 2009 but I assume the valuations haven't changed too much
http://www.forbes.com/lists/2009/34/soccer-values-09_Everton_340028.html