Okay, I know this is gonna get a lot of heat, but here's how they could do it in order to make me mark out like a little bitch:
Undertaker returns and wants revenge for being buried alive. He wants a rematch of the buried alive match. But this buried alive match will be different. This grave will be covered in flames and the loser will burn before being buried alive.
On PPV, Undertaker and Kane go all out trying to destroy each other. Taker wins by wrapping a bunch of chains around Kane to prevent him from defending himself. He then chokeslams Kane into the fiery grave. A microphone will be planted so we can hear Kane's screaming in pain. The screaming will go on for 2-3 minutes. We'll hear Kane begging Taker to help get him out. He could even say, "Mark, help me!" to make it more sincere/real. The Undertaker looks down the grave, almost questioning if he's gone too far. He will consider trying to help his little brother, but just when we think Taker is showing a little bit of remorse, he'll change his mind and give the signal to have the dirt dumped on the grave.
Kane can then take a vacation for 3-6 months to get in shape, freshen up. I'd have him return wearing his full-body suit which wouldn't show any skin whatsoever. But I'd have wearing all black, maybe a very small amount of dark/blood red colour on the front of his attire. He'd also be covered in the same chains that the Undertaker wrapped around him before throwing him in the grave.
He'd come face-to-face with Taker, no-sell anything Taker tries to do, and leave him lying in waste. I'd have one big final blow-off match with some crazy stipulation where new Kane wins clean, Taker gives him the nod of respect, and Undertaker disappears again until the next WM.
Feud over forever, and fresh, new, more-badass-than-ever Kane that I can enjoy watching again.
How would you guys bring back masked Kane, or would you even want to?