One thing they may want to consider is rolling over the 401(k) to a Roth IRA over a period of several years. They would calculate how much room they have left in the 25% tax bracket and roll that amount over to the Roth each year. They could even consider using up the 28% bracket as well, since 28% isn't that much more than 25%.
The advantage of doing this is twofold. First, there are no required minimum distributions from a Roth IRA as long as your parents are alive. Once the balance is rolled over, they can withdraw from the account if they want, or just let the account keep growing tax-free until they need the funds. Secondly, you can leave a Roth IRA account to your heirs, and they will also enjoy tax-free growth out of that account. One thing to note is that heirs do have required minimum distributions out of an inherited Roth IRA, so the heirs can't leave the money in there forever, but they also won't have to pay their current marginal tax rate on any distributions from that account.
Furthermore, if your parents have enough assets for the estate tax to potentially come into play, paying the taxes on this 401(k) money during their lifetime (instead of letting their heirs do it) should reduce the size of the estate and thus reduce the amount of estate taxes owed.
