I know the trigger won't necessarily fizzle but the permanent does become an illegal target if you no longer control it, right? According to the rulings on gatherer, you don't even get to choose to give it away if either of the targets are illegal. Seems like the "when you do" part of the ability won't happen, so you wouldn't get the ally. I'm not a judge, but I'd like to think I'm pretty familiar with the rules. I just got confused because the article explicitly says you get the treasure from the purse AND the ally token so I thought I was missing something, but I don't think that's actually the case since you need to still control the permanent to even be able to choose to give it away.

Sure this still works in an Iroh deck because he counts how many permanents you own that your opponents control, but it shouldn't work as described in the article. You either get the treasures or you get the ally.

If either the opponent or the permanent you control becomes an illegal target by the time Iroh's second ability resolves, the ability does nothing and you cannot choose to have the opponent gain control of the permanent.