Going by what general consensus shows, Joshua will beat Pulev and Fury will beat Wilder. Pulev is probably going to never fight professionally again as his age will probably not allow it and Wilder will probably not fight again if he gets beaten by Fury again because his ego will not allow him to risk a third defeat.
I don't think so, I've seen a lot of fighters who are beaten many times already but they are still fighting, of course if Wilder will lose, although he lose twice but it's just from one fighter only, and he can still fight another boxer that could still generate money for him. Boxing is more on because of money, not because of ego, or whatsoever, these guys are living a different lifestyle than the normal people, so they need money for that which they can only get when they will keep fighting. Wilder at 34 years, he still have a lot of fights left even if he lose against Fury.
The rest of your statement, I agree with it.
It's really up to the boxer himself on how he will take his defeat and move and fight another day. Another good case is Ricky Hatton, when Pacquiao beat his ass, he was never been the same. In fact, news surface that we went into depression after that loss, doing drugs and stuff and he never fight again. The scar the fight put on him mentally was too much to handle for him. Maybe he generated so much money throughout his career that's why he chooses not stay out. However, he admitted it after many years that it was really devastated on him psychologically. So we will see what happens to Wilder if he is defeated in the trilogy.