In reviewing the wikipedia list of airline liquidations from the last two decades, I would note Braniff, Aloha and ATA (not sure if the last one had a programme). I think my Eastern miles were absorbed into the Continental program, and as noted above PanAm miles are sitting in my Delta account, and TWA miles are in my AA account.

However, in absence of a merger or acquisition, it is likely that your miles would be history in event of a total liquidation. Though, as I noted above, I think that scenario unlikely for many reasons but particularly because the big 4 (DL,CO,AA and UA) are probably considered "too big to fail" like the banks and auto makers that were bailed out earlier this year.