Lately it has been 2 weeks of pay for every YoS with 45 days to accept or decline. As another commentor stated, that it's not really clear, your vacation if you are salary exempt is accrued on a month to month basis but was never conveyed to me upon hiring nor was it displayed on any pay stubs. But they will pay any unused vacation.
Is there an option of being hired back when the upturn in the market occurs?
The paperwork will state that you are available for rehire. Having said that I wouldn't expect to return to the company any time soon as the level of recovery needed to facilitate mass hiring is not right around the corner. Also, why would you want to return to a company that could not properly plan for these conditions? I would look outside of oil & gas for the long-term.
As far as your 401K goes, you can keep it in T Row Price for a fee, withdraw it and occur penalties, or opt to roll it over to a preexisting 401K or an IRA.
I personally opted to roll my 401K to the IRA in my credit union.