All depends on what your company’s official policy is.
http://www.labor.state.ny.us/workerprotection/laborstandards/faq.shtm#10
So basically, if they have it in writing somewhere that you get vacation but are not entitled to it if you are let go or resign, you have no legal standing to fight for it.
If however there is no written policy in regards to vacation time expiration or forfeiture, and there was a policy that granted you vacation time, you are legally entitled to it.