Based on my fairly detailed analysis of the ratings (and not just of AR) and assuming that this spring cycle has roughly the same performance level, I would expect a 1 cycle renewal and the show held as a back up (similar to season 12).
As for the ideas mention above of an all star season or a mixed fans versus favorites. On all stars I se very little chance of this. While all stars did perform worse then seasons 10 and 12, it still showed year to year increases over the last spring edition (season 9). But CBS was disappointed by those numbers. So I would say no.
As to a mix, I wont beat no chance at all. BUt that is based only on the difference in what the race is, compared to what surviver is. On survivor the game constantly changes, your team one leg might be your enemy the next. You also actively try and remove people you see as threats, something that is almost impossible in TAR.
And one thing almost every single racer has ever said is that the show is much harder then it appears. That would give teams that had already run a huge, huge advantage over new racers. From how to pack, to being sleep deprived, to how to interact with locals, what type of risks to take, how to maneuver with flights, how to beg and get assistance.
And the casting as always said they like to cast based on relationships (good and bad). They aren't going to cast people who don't know each other (certainly not all 11 teams).
The only thing I can see is them "stunt" casting. While they say they don't like to do this, I could see declining viewership be a factor making them change their minds.