I didn't have a Launcher2 app installed when I updated to 2.1, but I did install HelixLauncher2 (which is not yet Droid 2.1 compatible) so that I would get an update notification when it was made compatible with Droid. Still, for kicks, I ran the HelixLauncher2 and watched it give me repeated force close notifications. Between force closes, I manged to bring up the settings menu so that I could go to "Manage Applications" and kill HelixLauncher2 (and you can disable it as the default launcher while your there, too). Bottom line is, if you can get away from your home screen, it should stop force closing so that you can do something about it. Of course, if it's messed up enough now so that you can't get it to even go to the homescreen and start force closing, I guess you'll just have to factory reset it or something.
Bottom line is, if your launcher2 keeps force closing on the homescreen, there is still hope. Just get to the phone's settings menu in between force closes and you will be able to fix it without doing anything drastic.
-SR-