I personally would not consider a GM or Chrysler right now. But there probably are good deals out there if price is what you're after. My worries are not so much about parts availability - somebody (3rd party) will pick up the slack (or most of it) - but more about convenience. With all the dealerships being closed getting your warrantee work done might well involve a significant drive to one of the dealers that is still open. As time goes on, more and more dealerships will probably close and it might get more inconvenient. So even if GM and Chrysler pull themselves out of bankruptcy, you can count on less convenient warrantee work (fewer places to go), unless you happen to live near a dealership that remains open for the length of your warrantee. And there is no guarantee that you will end up in that lucky situation.

You also have to remember that 3rd parties do not currently make each and every part that's in an automobile. So it may be a while until some parts are ramped up and become available from 3rd parties, if they ever are. 3rd parties will be handling parts that they can make a profit off of. The manufacturers stock more parts because they realize that you'd never buy another car from them again if you couldn't get parts for the current car you bought from them. 3rd parties won't have this customer-continuity thing hanging over them, so they'll concentrate on the more common and profitable parts.

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p.s. - So what GM and Chrysler were worried about - nobody would want to buy a car from a bankrupt company - is true in my case. But what they didn't understand is that I would not have bought a car from a company that should have been in bankruptcy and was artificially held out of that state by bailouts. For me, "bankruptcy" and "should have been in bankruptcy" are exactly the same thing. I wouldn't buy from either. So save the taxpayers money and do away with the ill-conceived bailout.
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