I actually think Jack could be the perfect Santi replacement as the deep lying attacking midfielder in our system, as the latter starts aging. Granted Jack isn't as technically supreme as Santi nor have the same two footidness but not many players in football do though. Otherwise they share similar characteristics imo, good dribbling skills to relive pressure, fantastic eye for a pass to start and conduct attacks and good defensive closing down skills.
Also, given the new homegrown quotas announced it would be stupidity to get rid of him as even if he doesn't start when everyone's fit, he's still a quality player to have in and around the squad.
That being said, he really needs to contribute significantly next season and cut out the off-the-pitch shit. The fans and I imagine Wenger are starting to get annoyed with that and another season like the past two and a 35 million bid from City would seem very tempting indeed.