It's all on Undertaker if he decides to wrestle again or not. It's his life and people can complain all they want that they don't want to see him wrestle again. If he does then so what? People have come back from retirements all the time and it was never officially confirmed that he retired. WWE is leaving doors open and there's nothing wrong with that at all.
I wouldn't mind seeing a John Cena match with him before he hangs it up for good. I've never understood why the didn't do that years ago as I had it on my predictions for WrestleMania cards since probably 27. I remember reading a report it was supposed to take place this year but Vince nixed it as it wasn't looking towards the future to do that match. If that's the case then why did Triple H and Shawn Michaels face him for 4 WrestleManias in a row? WrestleMania is for dream matches and the biggest stage to do the biggest matches possible.
All in all if Undertaker does return for more matches I won't mind. If the guy feels up for it and feels good doing it then I respect him for wanting to continue entertaining me and I'm grateful for all the moments and matches I've grown up with because of him. Sting will never happen obviously but I would also like Sting to make an appearance during Mania season to cut a promo and some guys like I don't know the Miztourage come out to try and jump him then the gong strikes and Sting and Taker clean house.