1. It Will Help To Create New Stars
I've already mentioned how Lesnar retiring The Undertaker could take him to another level (if conquering The Streak made him powerful enough to take John Cena to Suplex City, imagine where he'd go from here...), but something the Phenom is past is being able to put over new stars. His match with Bray wasn't great, mostly because the younger Superstar had to significantly slow things down to accommodate the veteran, and so someone like Seth Rollins or Roman Reigns benefiting greatly from time spent in the ring with The Undertaker is unlikely. You know who both of those WWE Superstars did gain from spending time with in the ring? Brock Lesnar, after he broke The Streak! Reigns went into WrestleMania despised by fans and left with their grudging respect, while Rollins proved himself worthy of holding the WWE World Heavyweight Championship during that Triple Threat at the Royal Rumble and subsequent interactions with The Beast. After bringing The Undertaker's career to an end, anyone who steps into the ring with Lesnar and survives will gain the admiration of the WWE Universe, while the person who ultimately defeats him will be potentially propelled straight to a long term main event position! Brock can help get a whole new generation of WWE Superstars over, and unless you want to see many of your NXT favourites flounder on the main roster like Bo Dallas and Neville have, sacrificing The Undertaker's career at the hands of The Beast may ultimately be worth it, like it or not!