20m contract wouldn't be needed for the likes of Hodgson or Hughes. 6m over three years should be plenty, they'd jump at the chance to manage Liverpool. O'Neill might be 3-4m p/a, but again the opportunity would be attractive to him. So they could negotiate pretty hard, especially on the key part of the deal, the severance clauses. If you give him a 15m contract that you can cancel for 4m, on paper, the liability is 4m, not 15m.
The key to making the club attractive would seem to be having a committed manager in place who can be got rid of cheaply if the new owners so desire. That, and cutting the ongoing losses right back, whilst investing in some young players.
I cannot possibly see RBS leaving Dalgleish in charge, he's just not a safe pair of hands for their investment, he could easily lead them into the bottom half of the table, damaging the image of the club further.
I imagine one of the three named above will take over within a month, Mascherano, Torres and Reina will leave, and he'll get 50m plus to rebuild. The wage bill drops to a level managable without champs league money, they look like a superior top 6 team with the potential to be much much more if the investment is made.
The alternative was to keep Benitez and all the players, sell them as a top 4 club who had a blip. but no one is willing to subsidise the 40m a year until a buyer can be found, and no buyer will be found whilst the team is running at a huge loss, work on the stadium hasn't even begun, and the price is still 500m. RBS want their money back, they would be happy for it to be sold for 350m because it's the yanks who will take the hit.
IMO Benitez was leaving anyway, he knows what's happening, they just paid him off so it looked like they were restructuring rather than being dumped.