I have a Rufflet (bad choice so far) who is level 50 and I really want it to evolve to Braviary, so I gave it an Exp. Share and am grinding on the Elite 4. I've spent all my money on various items and I don't care about using Return on any of my Pokemon, so I have little to lose from fainting them repeatedly.
My main concern is that I might black out in the battle where Rufflet finally gains his 54th level. Would he still evolve to Braviary in this case?