[...] but UT in general is suffering population decline.
Actually... I also thought that to be the case until a good while back when I checked actual numbers:http://steamcharts.com/app/13240
and yes, these are from Steam, and so there are actually more players playing the game than that, and not necessarily online either.
However, it shows that although it's a very low population, the overall player count has been rather stable throughout the latest 5 years (if you go that far in the chart).
And with UT4 with an uncertain future as of now, whoever wants to play UT will generally try out the classic one, and there are new players on Steam posting on the forums over there simply about the problems everyone already knows about (game too fast, mouse smoothing, bad renderer, etc).
If these problems become non-issues someday (as in, getting everything up and running with a single patch for example), these are new players which might actually stick around and increase the population a bit over time.
This doesn't mean UT would "revive" or anything, it just means that it's not in as a bad shape as you may think, at least for the time being.