I wish I could get behind this, but it's pretty wishful thinking IMO. Even if Duncan/Manu both come back, they'll be another year older and likely worse than they were last year. If Duncan doesn't come back, we're going to be struggling to land a starting caliber center. Parker and Diaw both aren't young and will be 34 next season - it wouldn't be shocking if they suffered a bit of a decline.
Even if those things you mentioned do happen (Kawhi improves even more, DG bounces back, etc.), I think it's pretty unlikely that this team is good enough to win a le next year if the plan is to just bring the same team back but with some new end-of-the-bench guys. It would require a lot of things going right with the bench (KA becomes a legitimately solid rotation player, Bertans proves to be a capable NBA player and contributes, Boban steps forward and becomes a legitimate full-time backup C).
Guess we'll wait and see what happens this offseason though. Maybe they manage to land a solid ringchaser on a vet minimum deal or something.