Question is... would a star level player like to play for the Raptors next year?
That's the same question that OKC faced when they traded for PG13 last offseason ......... OKC is a small-market team & isn't a hotbed for FA's - but Sam Presti saw the 2017-2018 season as an opportunity to try to convince PG13 to re-sign with them. It worked.
It's the same situation with the RAPTORS and Kawhi now ....... 1 year to try to win the EAST and convince Kawhi to take their max-contract offer (bigger than any other team can offer) next offseason.
There are no guarantees in the NBA ....... GM's prepare their teams, balancing roster and cap space / flexibility.
Likely, how the RAPTORS perform this upcoming NBA season will play a big part whether Kawhi re-signs or not ......... not to mention that RAPTORS have the most money to offer Kawhi (on the downside, Toronto has one of the most highest income tax rates among NBA teams).
Best case for the RAPTORS, they re-sign him and it attracts those 2nd, 3rd-tier stars. fringe & rotational players who wants to be part of a winning team.