CubeCraft is planning to update to a minimim version requirement of 1.12 in the near future (I hope at least lol), so what will happen to all the runs that were done in 1.8?

I personally feel like these runs will, once the update drops, have an unfair advantage over other runs (At least for the World Records), similarly to the fact that seasonal maps are banned.

Are these runs gonna be moved to a different category, gonna be archived, deleted, or will nothing happen to them?

Well, nothing changed when the kb / entity / queueing update came out and that was huge, so it might just be that nothing happens to them if the mods use the same system as last time.

I can't imagine that the runs will be completely, but based on precedents I don't see the leaderboard getting split, so probably nothing will really happen to the runs. At least that's what I'm guessing.

It is something that we would have to discuss, but something I think may happen is not in an entire removal of the 1.8 runs but splitting them off in a dead category. If we find this to be to much work we will most likely remove them and change Java to 1.12

Most of the runs I think are on 1.9 or above, so I don't think it will cause too much of an issue.