How long before a UI Mod can be officially considered abandoned?
 

When I took over ThorUI, faetyl had stated there'd be no more updates and left the files for anyone who wanted to take over. So I wasn't worried about that.

But there's other UI pieces that I'd like to intergrate into Thor, and the creators have apparently left EQ2Interface, if not EQ2 entirely. I admit, I'm lazy, and I'd rather pull together pieces that do what I want than recreate the work someone else has already done. I credit the sources, and once I take something over I handle maintenance/updating myself.

So, at what point is it considered acceptable for someone to take someone else's UI mod, when the creator can't be reached to ask permission?

There are no express rules for that on this site. Technically nobody waives their authors rights by uploading here, but practically there is a spirit of collaboration in this community.

As long as the creator has not expressly stated to you or the public that they do not want their work to be touched then my personal stance is that you are fine in doing so as long as you give credit. If you want to change the source substantially you should rename it and continue it as your own (what's known as a fork in the OSS world).

As to a time period to wait - if you have the feeling that the creator has left this site the waiting period has probably been long enough.

Practical example: Not counting ProfitUI itself, the two other cases that I remember integrating mods from authors that had been on a hiatus (one I did a full integration/rework, the other I did upkeep the original source as well) both authors did pop back in here eventually and both did actually thank me because they were happy their work was still being used.

Just give credit where credit is due.

Thanks for the feedback, it helps a lot!