lol Taker wins a match where his career is on the line, and then he ends up retiring on his own afterwards anyway? That would just make the whole Undertaker/Shane/Authority storyline even stupider than it already was.
If The Undertaker was retired, WWE would be making a huge deal out of it and at the very least be publishing the news all over their website, even if the man himself Mark Calloway didn't want to make a big hoopla out of it. Also, as mentioned it was announced weeks ago that Taker would be on WWE's European tour in a wrestling capacity, so we've known for sometime that he wasn't gonna be done after Mania.
That said, I personally thought this year's Wrestlemania would have been the perfect time for him to retire. "Biggest Mania of all time" (though it was nothing of the sort), it's in Texas, Taker's up there in age, Streak is long dead, etc. If they stuck to the original plans of saving Brock/Taker III for WM instead of blowing it off at Hell In A Cell, that would have been an excellent way to bow out with Taker's career on the line. Then Heyman could brag about how Brock used to be the 1 in 21-1 and is now the 2 in 22-2.