[Coda]

I am not a lawyer, and this post does not construe legal advice, only personal advice.

They CAN'T force you to stay working for them. That would be slavery, or at least indentured servitude, both of which are illegal in the US (and I imagine most other developed countries).

Look at your contract. (Yes, you have one.) Look at what the severance terms are -- it should specifically say in the contract what they are and aren't allowed to do if you violate it. If you can deal with the penalties listed there, you can just quit. Odds are, the only penalties listed in the contract that they can actually levy against you are termination (what are they going to say, "you can't quit, you're fired"?) and MAYBE garnishment of wages (which is potentially illegal depending on the specific circumstances).

Keep your eyes open for other sleazy behavior they might pull -- in some states, it's illegal to withhold your final paycheck or to deduct from it to cover debts owed to the company. (I had a former employer pull this stunt. I took them to court over it. On one issue, they settled before it went before the judge; in another issue, they didn't even bother showing up in the courtroom and I won the case.) If anything they do seems fishy, look into it!

Now, one thing they CAN do if you quit is to deny you unemployment benefits. Of course, if you have another job lined up, this doesn't really matter.