Let's say I land on someone's hotel. I'm short in cash. So, I sell houses, mortgage everything, and am still short in cash. I am now out of the game and that player gets my money and mortgaged properties. If I remember right, they pay the 10% tax or unmortgage at that time. And the game continues.
Now, let's say I had just barely enough cash to pay them. I'm safe and still in the game. I've got nearly zero money and all my stuff is mortgaged. The next turn I land on chance/community chest/luxury tax/jail and I need to pay the bank. I cannot pay.
Who gets the properties? Do they disappear from the game? Go back for sale as mortgaged? Unmortgaged?