More teams are coming. At this point, it's inevitable. Adam Silver has been talking about it for years, and the Board of Governors is set to vote on adding two teams this summer. When they inevitably decide to move forward, an expansion draft will come soon after. The new additions will get to fill their roster with players from existing teams, and the Spurs will have some important decisions to make.
There hasn't been an expansion draft in over 20 years when the Charlotte Bobcats joined the fray, but the rules likely won't change too much.