They could take steps to down scale the entire site until they could support it themselves with only their own funds, and possibly donations using cash or crypto. Though even here people who paid for their games should be able to play and redownload them.
No it doesn't. It means stopping all purchases on the site until you set up your own payment processor. No games would be removed. Unless you mean people who don't already own them not being able to buy them in the meantime.
They haven't tried it so you cannot say it can't work. Let's not act like some sites don't rely on donations. I'm not talking about paying devs while doing this, just paying for server costs.
You are suggesting something along the lines of "Power went out? Make your own power grid that supplies your entire region!"
This is not a feasible solution for basically anybody.
Of literally every entity affected by this, to date, literally only Valve could maybe pull it off. Because it takes a fuckton of money, time (time you're making zero profits during), and getting a lot of banks to cooperate with you (which also takes a fuckton of the money you're rapidly losing).