To whom are we addressing the prayers? God is not bound to time. He can make our prayers efficacious, even if it is an efficacy that violates our experience with time. I hate to think that any prayer is unproductive.
So is the dead person - and this is more important - his life is OVER, and his chance GONE. If we say "I pray that he found repentence before he died," then that is valid, but only in the realm of hoping, not for effecting change.
Here we more or less agree. Thanks for the discussion.
SD