GM has a market cap of $1.7 billion. Ford has a market cap of $3 billion. Cerberus would probably pay you to take Chrysler off their hands. $5 billion or so out of the retirees' health care trust fund that you administer would buy the whole Big Three. Fire the management and run it yourselves.
Seriously, it may be in the UAW's own best interest to just buy GM, due to the terms of the current collective bargaining agreement and the fact that 73,000 UAW members who work there will be out of a job if it goes bankrupt and is liquidated. Besides, it's altogether possible that the employees could do a better job of running the company than the morons in charge now.
When the UAW took over the pensions of retirees last year, a big chunk of the funding was GM stock, which is worth practically nothing today. GM's management got the best end of the deal. The $30 billion in cash that GM shelled out to the UAW when it turned over the liability of paying for the retirees' health care was just 60% of the amount that they would have had to pay the retirees if it hadn't passed off the responsibility to the UAW. The only way for that pension fund to recoup its losses would be to buy the company, make it profitable again, and thereby make the shares valuable again.
It won't happen, but it's a thought. :)