I promised a start to one of my freshmen and intended on fulfilling the promise for the majority of the season. However, after sitting 4 of the first 9 games (no pattern) I got the letter stating he was unhappy along with a 26 point drop off in WE. I now intend to start him for the rest of the season. Am I stuck with this huge drop in work eithic? Or will it jump back up to normal at some point if he continues to start?

my friend did the same thing, and the work ethic dropped like high twenties or low thirties, and now is almost back even since starting him every game from that point

you probably will recover all or most of the WE

keep in mind - the promise is not a majority of the starts - the promise is all the starts.  Long ago, one could reliably satisfy the player with 80% of the starts but they changed that and now it takes more - usually. 

Also keep in mind that you can keep his minutes low by using target minutes to run your depth chart - most folks would say that is less effective than fatigue based subs, but one can do it - and limit a kid to apx 8 minutes but still starting.....IF you want that and are willing to work at managing the minutes

Another way to do it instead of using the target minutes is to set him to fairly fresh for fatigue and set his backup to getting tired or tired.