As to what happens if they miss December 31st, if there are enough refund requests, especially with legal backing (and this appears to be the case), and they don't have the coins/cash to refund, then I suppose they file for bankruptcy and/or sell themselves, or part of themselves, to somebody who wants the tech and can take on the liabilities.

Or they sweeten the MPP so much that they defuse the situation with enough customers that they can wiggle out by refunding some and placating others with promises of future hashpower.