Would I be entitled to any portion of the 401K benefits after he passed?

The issue of your interest in his 401k should have been dealt with in your divorce..If you and he chose to represent yourselves and did not give you an interest in his 401k, once you were divorced he had the right to change the beneficiary of his 401k. You only have an interest if you were given one in the divorce judgment and other appropriate orders were entered.