I don't agree it makes the Wrestlemania match useless. That's like saying Wrestlemania makes Summerslam useless. I know the argument is that since HHH got his revenge in the second bout, that would make him losing cleanly the next time somewhat useless but that could possibly be construed as looking too deeply into it. Besides, one of the scenarios I constructed in my firs post was HHH having it won by escape but he doesn't take the chance because he wants to pin Brock. But he also plays it cocky. He has Brock down on the mat for awhile and teases walking out the door but then steps back in the ring. After maybe dishing out some more punishment on Lesnar, he slowly climbs the top of the cage and makes it look like he's climbing over, but then climbs back down, once again playing it arrogant. He then sets Lesnar up for more punishment (a pedigree to finish him off finally perhaps) but then Lesnar springs to life suddenly - similar to the Summerslam ending - and hits him with an F-5. Probably will take more than one to put him down. This way, it can look like HHH had it won but only by escape, which isn't a definite of a win as pin fall or submission, but still cost himself the match regardless. Hell, they could even make it look like Lesnar could have escaped the cage earlier but didn't take the chance.
He could say the next night on Raw that he got too confident from knocking out Brock Lesnar at Wrestlemania and throwing him out of the cage on Raw that he ended up costing himself the match. He should have known not to take someone of Lesnar's stature lightly this would be neat, showing Lesnar a bit of respect in a "I hate you, but still respect you" kind of way.
IF anyone interferes, bank on it being The Shield since they've already teased it.