Here's my opinion: Shafer's career at SU is going to be tied to whether or not he can find the right offensive coordinator. If Lester isn't up to the task, I see Shafer's decision to stick with him as being very career shortening.
Shafer IS a defensive guy, like you mentioned, and for all of his positive attributes he brings to the table as a HC, he doesn't seem to have a concept on what offensive identity he wants to have [which is really weird, because he's a former college QB]. So, like most successful defensive oriented head coaches, the selection he makes at OC is very important to offset that "gap" / hole in his coaching apptitude.
If Lester's offense works as well as suggested, then the ship will be righted this year. What does that mean in terms of on-field performance? That's tough to answer--but it probably means winning enough games to qualify for bowl eligibility. At minimum [if the unthinkable happens and we don't qualify, but get close with like 5 wins], then the offense needs to show so much promise that the new AD doesn't pull the plug.
Because the alternative is that the offense is as generally dysfunctional as what we've suffered through lately, with no indication that improvement is likely, and that would and probably should cost Shafer his job.
I like Shafer--a lot. I think he's got the right personality for CNY, I think his attitude can fire up the fanbase, and I think he and his staff are above average recruiters who can help replenish our program. But I also think he needs to win in order to prove that he is the guy for the job. As encouraged as I was after year 1, I'm as concerned about Shafer's ability to game plan / game coach after year 2. This is a big year for him. Given our success on the recruiting trail for the class of 2016, I'd really like to see what Shafer, Lester, etc. can do once they've recruited kids for their system and stocked the cupboards with playmaking talent that the team currently lacks.