Oh, man, you really fucked up. Here are the packages which depend on upstart, and which would have been removed accordingly when you removed it.
met% apt-cache rdepends upstart
If I were in this situation, I would probably reinstall. The alternative I would try first would be
1) Boot from a live CD
2) Mount the hard drive
3) chroot into the hard drive
4) apt-get install upstart and the above packages.
But it's not guaranteed to work without a lot more that 3 BTC of effort (or even 20 BTC, at least the way I figure my own time.)