Could the oil well itself collapse?

All of these things lead to only one place, a fully wide open well bore directly to the oil deposit. After that, it goes into the realm of “the worst things you can think of”. The well may come completely apart as the inner liners fail. There is still a very long drill string in the well, that could literally come flying out. As I said, all the worst things you can think of are a possibility, but the very least damaging outcome, as bad as it is, is that we are stuck with a wide open gusher blowing out 150,000 barrels a day of raw oil, or more. There isn’t any “cap dome” or any other suck fixer device on earth that exists or could be built that will stop it from gushing out and doing more and more damage to the gulf. While at the same time also doing more damage to the well, making the chance of halting it with a kill from the bottom up less and less likely to work, which, as it stands now, is the only real chance we have left to stop it all.

via The BP Deep water horizon, Macondo Well Blowout. and what we are facing in the Gulf Part II.