In the last 30 years we've had a great QB have 9+ wins in their last season 6 times. Once (John Beck to Max Hall in 2006-2007) there was no dropoff, but every other time there was a dropoff ranging from medium (94 to 95) to massive (01 to 02).
Hopefully Conover (or Hall or Romney) can come in and keep it going, but odds are stacked against it. Right now my line for next season is 8 games. If we win fewer, it's a disappointment, if we win more, it's a success.
1994: John Walsh led BYU to 10-3 in his last season; 1995 BYU went 7-4.
1996: Steve Sarkisian led BYU to 14-1 in his last season; 1997 BYU went 6-5.
2001: Brandon Doman led BYU to 12-2 in his last season; 2002 BYU went 5-7
2006: John Beck led BYU to 11-2 in his last season; 2007 BYU went 11-2 (Max Hall)
2009: Max Hall led BYU to 11-3 in his last season; 2010 BYU went 7-6
2016: Taysom Hill led BYU to 9-4 in his last season; 2017 BYU went 4-9