When it all boiled down to the crucial moment, Zuko still wanted his dad's approval most and afterall, he's firenation...So I don't think its a plan, he really helped Azula. But being the evil witch she is, Azula will probably test Zuko by executing Iroh in front of him or even asking him to kill Iroh himself, and Zuko will hesitate and in the end free Iroh or something...Coz I don't think Azula really wants to offer Zuko "redemption"...

hmm.. I think Zuko will in the end probably saved by Iroh in the end.

The reason is because of the death of his son Lu ten that he wasn't able to protect, I don't think that he will let this happen to Zuko (who he treats as his own son) just a theory by the way

In the short run I think zuko will probably free Iroh because of the guilt he had on betraying his beloved uncle