I left a company to go back to school (took on massive loans). A few months later, the company closed up and people got extremely generous severances. Would have probably covered half my tuition costs. I definitely wish I had stuck around THAT company longer!

Which illustrates the original point: that scenario -- generous severances when the company is going out of business -- is incredibly rare. A much more likely scenario is your options become worthless and you're laid off. If you can leave a bad environment, I recommend leaving ASAP instead of letting the golden handcuffs keep you -- unless the golden handcuffs promise a huge return, and there's little or no doubt about getting that return.

I know a few folks who have left jobs and then said "I wish I had stuck around that company longer". In all cases, it was never financial. Rather, it was "If I'd known what I didn't know, I would've stuck around longer so I could pick <ex-coworker>'s brain about it."

Even in my own case, where I joined a company thinking I'd leave after a year but stayed 5 years because I was still learning things (and had optimized my career for learning the whole way), there were still some times after I left where I thought, "Man, if only I still had access to <old design doc or code>."

I see financial motivations coming up much more often when people say "Man, I'm glad I stayed." Vesting cliffs are really easy to predict, and even IPOs and acquisitions have some hints coming; if you're about to get a major windfall, you'll probably know it.