We just don't. I like it, but if the rivalry ended I frankly think the U's program is worse for it than the Y's.
The Y will always be relevant due to its mission and built in fanbase. The U needs something more to be more than an also-ran Pac12, regional school. I ask if 10 years into the future if BYU were still in the WCC and never played the U, would I care? I think the lack of a series would be a monument to silliness by the U, but otherwise, meh. BYU would continue to have success, just on a different stage, but to its growing national audience. The U would have its Utah fans and that's about it.