I'll have to ask Saltlover on this, but I had a discussion on this that had the Raptors potentially getting two max slots for 2020's FA+a bit more cap if Kawhi bolts. If this is true, this is an awesome deal for Toronto as it improves them this year for contention and allows them to properly rebuild if everything doesn't work out by tanking for a year or two and then go for big FAs.
Yes, assuming this deal happens (and it’s unclear what is in addition to DeMar/Lowry, but there’s something because the salaries don’t work), the Raptors look to only have Powell and Anunoby under contract entering the summer of 2020 (plus any other draft picks they make). So they would certainly have room for two max players and the ability to add a role player or two with cap space. And if they hang onto Kawhi, one max player. All that said, I’m not certain what the free agency market will look like in 2020, both in terms of available players and bidding competitors.
Also, if Kawhi leaves, they will not be a tax team next year. With Derozan, they likely would have without additional moves, so there’s a mild benefit there. They could potentially tank for a season by doing a sell-off, or they could keep competing as a mid-level playoff team before rebuilding in 2020 free agency (kind of like the Celtics last off-season).