The meaning of "lifetime" is an agreed-upon term. If this developer decides that the word means something different, that's not what the buyer has agreed upon

The meaning of "lifetime" is an agreed-upon term. If this developer decides that the word means something different, that's not what the buyer has agreed upon based on the wording of the license being sold. If you don't actually want to support something until you die, then don't offer lifetime licenses. If you do offer that license, don't act surprised when your users interpret that with the common and dictionary definition of that word.