Would your reaction change if Daniel Bryan was the one who took the Summerslam beating as apposed to John Cena?
I think that the reaction of most people would've been completely different and very negative. According to reports, Bryan was planned to be the one who took the decisive, one sided beating & loss that Cena took. John Cena's legacy in WWE has LONG since been established over the past 10 years in the sense that he could've gotten in absolutely no offense whatsoever against Lesnar and it wouldn't have hurt Cena's image in the slightest. Vince McMahon, however, believes that Cena has to be this nigh unstoppable human juggernaut even though a good number of fans are genuinely burned out on that. The idea of Cena being vulnerable is one that people haven't really seen and it was an intriguing idea, but Vince got paranoid that people would lose faith in Cena.
However, if Bryan had taken the loss, I think there would have been a very negative reaction. Bryan's legacy isn't as stable as Cena's, though there are very, very few in the history of WWE with as secure of a legacy as Cena. Bryan losing in that sense would've resulted in some fans going the route of saying "WWE just buried Daniel Bryan" or "WWE blew an opportunity to cement Bryan's long term status as a main eventer" or "Lesnar doesn't deserve to be champion because he doesn't love the business and is a part timer" arguments. Bryan's fresh and is someone that fans have wanted to and enjoyed cheering for partially because he doesn't fit the usual mold in terms of physical appearance that Vince has a preference for.
I wouldn't have agreed with the notion that WWE would've been burying Bryan, but I'd be more inclined to go in the direction of them missing an opportunity to further solidify him. Whether or not they truly were gonna go the route with Bryan that they went with Cena will never really be known.
What would Daniel Bryan be doing after Summerlslam?
As a former champ, Daniel Bryan would've had a rematch clause, I think he has a title bout at some point as he didn't technically lose the title but that's neither here nor there. Bryan & Lesnar would've had a rematch for Night of Champions though, again, we're left with the question of who ultimately walks out as champ. In Bryan's case, since his legacy isn't as secure as a main eventer, would be viewed as an even bigger underdog while, simultaneously, the terms of Lesnar's deal are a major factor just as they currently are with Cena's rematch. The notion of Lesnar retaining the title seems unlikely because of how his deal is structured, yet we're left to wonder if Lesnar retains because he had such a lopsided win over Cena, if more dates have been added to his deal, if Seth Rollins will cash in his MITB briefcase, etc. It'd be the same if Bryan was healthy and the one facing Lesnar.
In Bryan's case, losing to Lesnar and managing to redeem himself by reclaiming the title at some point MIGHT have placated fans. If Daniel Bryan ultimately slew The Beast Incarnate, I think fans would've eventually been okay with a SummerSlam loss. In the case of Cena, if Lesnar loses to Cena this Sunday, it'll be business as usual with Super Cena rising to the occasion yet again and having to endure another John Cena title reign that I don't think a whole lot of people are especially anxious for. Even some people who're major supporters of Cena are burned on him as champion, so Cena walking out at NOC as champion will be viewed as anti-climactic for a lot of people.