#4 Dean Ambrose
Alright, so this one is no real surprise, but still worth mentioning. Former WWE Champion and founding member of The Shield, Dean Ambrose was revealed to be leaving WWE this past January. The news spread around so quickly throughout the internet that WWE themselves acknowledged it to be true. They would even go one step further and even mention his pending departure on television also, as he wrestled a series of matches putting over other superstars.
So while it is no shocker that WWE chose to keep Ambrose off of WrestleMania and save his final WWE appearance for RAW the following night, it is still somewhat feasible that Ambrose could have made an appearance at 'Mania to have one last ride with The Shield. Ambrose could have aided either Seth Rollins or Roman Reigns in their matches with Brock Lesnar and Drew McIntyre, respectively.
It would have given yet another great moment for the show and ended a great WWE run on a solid note, on television at least. Ambrose did receive this kind of send off, when RAW went off the air the following night.