IIRC, one who was sentenced to death is considered already dead (גברא קטילא)(San 85a, but exact source needed) (or is it only about losing his property?).
When G-d sentenced all 20-60 y.o. Jews to die in the wilderness: (Num 17,29):
בַּמִּדְבָּר הַזֶּה יִפְּלוּ פִגְרֵיכֶם וְכָל־פְּקֻדֵיכֶם לְכָל־מִסְפַּרְכֶם מִבֶּן עֶשְׂרִים שָׁנָה וָמָעְלָה אֲשֶׁר הֲלִינֹתֶם עָלָי׃
In this very wilderness shall your carcasses drop. Of all of you who were recorded in your various lists from the age of twenty years up, you who have muttered against Me
Shouldn't it automatically exempt them all from all Mitzvos as already dead? Or, because the generation was sentenced by G-d it has a different status?
If you have a source that my assumption is wrong, please let me know, I'll delete the question, don't just downvote.