Wow, I hate quitters. 
I feel bad for Heidfeld though, as someone pointed out already, I doubt he'll get a ride after this.
There will be plenty of opportunities for Nick, I reckon. If Nico ends up going to McLaren, he could end up at Williams. He could also replace Fernando at Renault, should the Spaniard leave, although I imagine Kubica would be higher on their list. McLaren could pick Nick up, too. It would certainly solve the problem of Mercedes wanting a German driver if Rosberg does not move; Heidfeld would be a better choice than Sutil and I don't think Glock is going anywhere. There are also three new teams who will be in need of experienced drivers who can be counted on to bring the cars home safely. Heidfeld has currently been classified in thirty seven consecutive races. How could you argue with that record?
Finally, there is whoever buys BMW Sauber (assuming the team is sold). I think for the sake of continuity they would attempt to keep the current drivers (or at least one of them) onboard. If Peter Sauber is the one that takes over, I reckon he'd keep Nick.

On to your other point, I dislike quitters, too.