With less than half of LDS residents actively participating, Utah is currently about 1/3 Active LDS, 1/3 Ex-LDS and, 1/3 Non-LDS. Active active LDS will likely <25% in the next 20-40 years.
The other question is how much of BYU's non-Utah student population is more than a generation or two removed from an explanted Utahn who attended BYU? Will BYU's draw for out of state LDS kids hold up after more generations outside of Utah, and will recent Utah explants who did not attend BYU still send their kids there?