Tribunal isn't a thing these days technically, but rioters deal with stuff with the aid of fancy machine learning systems.
I believe only those in the most recent game they were reported in get a notice, and possibly only for more extreme punishments (i.e. perms). Intent feeders generally are the sort who do it in mulitple games, so your specific game might be just one game of evidence out of many, and it's possible the they ultimately got punished for a later game. (Also possible that a rioter hasn't actually gotten around to reviewing things yet.)
Theres also the possibility that despite their threat to feed, they didn't intentionally follow through, and it actually did end up being a bad game on their part. Plenty of people out there who are all talk and try to coerce people to play their way with threats along those lines with no genuine intent to feed (I think they can potentially get punished for that sort of thing too, albeit probably more minor than actual intent feeding).
Regardless, it's probably best to move on. You reported them, so riot will sort it out from there eventually if needed. People get caught up and semi-tilted in quests for justice/vengeance but it rarely does anyone good to dwell on bad things/people when theres nothing more to be done, and sometimes people will get a bit carried away and end up breaking rules themselves, as another persons misbehavior isn't a free pass.