Hey Matt,
In order for this to work, you'll need to let the SDK know that you're replaying your video. Right now the SDK can't differentiate between what you're doing and a user just seeking from the end of the video back to the beginning (in which case you probably wouldn't want to show them ads again). For this to work, when your video is done (the first time) you should call contentComplete on your IMAAdsLoader instance and, after post-rolls (if any), destroy your IMAAdsManager. Then seek back to the beginning of the video and request ads again the same way you did the first time the video was played, with the same AdsLoader and AdsRequest objects you used the first time around. You'll get a new instance of the AdsManager in your adsManagerLoaded delegate method. Give this a shot and let me know if it works.
Thanks,
Shawn Busolits
IMA SDK Team