Depending upon when exactly they're bringing Ambrose back to television, I'd probably end it at Survivor Series if he pops back up in time to make his presence felt at Night of Champions. I could see the title situation at NOC go down like this:
I'm thinking that Cena vs. Lesnar at NOC will be more of the equal, back & forth brawl we were expecting at SummerSlam. As a result, no matter who wins, the winner will be exhausted. Rollins could attempt to cash in and come within a hair of doing so, only for Dean Ambrose to pop up out of nowhere and screw Rollins out of yet another opportunity. It'd seem sort of poetic really and would immediately restore heat to the feud since Rollins waited all this time, had the perfect opportunity and Ambrose suddenly shows up to spoil his plans yet again.
This leads to the feud picking back up with the two of them ultimately meeting at Hell in a Cell in which Ambrose is ultimately able to pick up his first win over Rollins. In order to even things up at 2-2, I could see them having a final match at Survivor Series IF WWE doesn't go the route of including them in a traditional Survivor Series 10 man elimination tag team bout. For the heels, I could see the team consisting of Triple H, Kane, Randy Orton, Seth Rollins and POSSIBLY Cesaro or Miz. If Triple H doesn't compete, I could see both Cesaro & Miz being put on the heel team. The babyfaces could be made up of John Cena, Roman Reigns, Dean Ambrose, Sheamus and Dolph Ziggler.
Of course, as I said, it all depends upon when Dean Ambrose finishes filming his scenes for the movie he'll be starring in. If not in time to make his presence felt at NOC, he could still pop up sometime before Hell in a Cell or possibly in time for Survivor Series, which could lead into TLC. If it does extend to and end at TLC, I personally hope it's not for Rollins' MITB briefcase. While it'd be an entertaining match, it's also one of those situations where logic suffers a brain fart because Ambrose would have everything to gain and nothing at all to lose. All Ambrose could put on the line would be his career, which makes it even worse because it telegraphs the ending of the match the very instant said stipulation is named.