listen, i'm not happy with Bronco's performance this year either, however canning a coach with a career 70% win percentage sets a program way, way back.
After Tom Osborne Nebraska hired Frank Solich (i think that was his name). Nebraska hired that coach after a couple years with a 70% winning percentage. Nebraska couldn't find a good replacement for Solich (they settled on Bill Callahan IIRC) and struggled seriously.
BYU doesn't have the pull of a Nebraska, and has significant limitations that Nebraska doesn't have. BYU has to deal with academic and honor code issues that coaches will recognize could seriously impact their ability to craft a winning program.
BYU needs to be careful not to blacklist their program from potential high quality football coaches.
Has Bronco done well this year? absolutely not...it's a gargantuan failure, but let's not make a single year failure into a 10 year program set back