What is going to generate more headlines for the WWE? "Undertaker retires unbeaten at Wrestlemania" or "Undertaker loses at Wrestlemania". The fact is that WWE will probably get even mainstream news coverage for an Undertaker loss at Mania. It has got that big. If the loss was to happen then the internet and media would light up with news stories and features on the loss. WWE could ride that momentum for months on end.
The loss of the streak is the kind of unimaginable event that would bring even lapsed fans back into looking at the company. The more casual fan needs to be offered something beyond the ordinary in order to keep on coming back to tune into the product. A Taker loss at Mania would almost certainly have more fans tuning into the next nights Raw as opposed to the number of fans interested in tuning in after the standard Taker win.
Great wrestlers go out with losses. Look at Shawn Michaels. The best way to end any pro wrestling career is to finish up by leaving it all in the ring. This is what The Undertaker needs to do at Wrestlemania 30.