Depends on the specifics of your particular plan - you can check with the plan admin to see for sure. In some cases the beneficiary may be allowed to keep the 401(k) assets where they are, but this is not common. Most plans require the beneficiary to take the money out as a lump sum. If the beneficiary is a surviving spouse, he/she is allowed to roll the assets directly into an IRA without having to pay taxes (until such time as the money is withdrawn from the IRA). This option is only available to a surviving spouse - if someone else has been named the beneficiary of the 401(k) - such as a child - and the plan requires that the 401(k) assets be withdrawn, then they have to take the assets as a lump sum and will have to pay income taxes on it.
Here's a good site for more detail:
401khelpcenter.com - What You Need to Know When You Inherit a 401k (http://www.401khelpcenter.com/mpower/feature_2beneficiary.html)
As for losing a job due to plant closure - you should be able to keep your 401(k) where it is, although if the amount is small (less than $5K) they may require that you take a disbursement. In this case you can roll the assets directly to a rollover IRA without paying any taxes or penalties.