I love the BYU rivalry and hope it doesn't die. As a Utah fan, it was incredible to play USC, Stanford, Oregon, UCLA, and Michigan all in the same year. Every game in the PAC12 is an awesome "big time college football" experience - win or lose - and obviously 100 times better than the old days when Wyoming, UNLV, San Diego State, etc. would come to Rice Eccles. But personally, not playing in a rivalry game, a true rivalry game kind of sucks.
Michigan has three true rivals (Ohio State, Notre Dame, and Michigan State) and I would love to see Utah get there as well - it does not have to just be BYU. Although the BYU game should happen every year. Hopefully the Utes get back to playing the Cougars consistently, Colorado turns into something (maybe a fight needs to break out at the end of one of their games), and maybe Oregon State with Gary Anderson will turn into a great rival- I could see it. The last two or another team from the PAC12 will take some time to develop though.
Point being, I don't think a majority of Utah fans want to see the BYU game go away. Those who pretend like they don't care are just pushing buttons and talking smack. For most Utah fans, its way too much fun beating BYU to have that game just disappear.