I was going to speedrun Hexen 2, but saw that the last mod login was 5 months ago! And the other a whole year! I get its not a very popular game with few runs but don't think they'd be suddenly returning to accept my run ? I'll submit my first run, but what then if the mods don't see it ?

Submit the run. The mods might have email notification enabled and could come back when they’re notified there’s a run to review.

If after a few weeks they haven’t logged on, then message them through the linked social media in their profiles.

And if they don't respond then go to the support hub, then go to game and series request, then report inactive moderator and request to be a moderator.