Durant and Curry are injury prone. Draymond is undersized so once he loses a step he won't be the defender he is now, but will still keep flapping his mouth.
Even against the full strength warriors, I think the Spurs would have had an outstanding shot had Parker and Kawhi not been hurt. Im curious to see if Cleveland can push them at all. How unbeatable are they really? I don't think anyone knows for sure.
I think they likely have a 2-3 year window. Eventually an injury will derail or personalities conflicts will arise and someone will walk for more money or to make their own name.
Even if they do stay healthy and together, I think the NBA will change the cap rules to break them apart, especially if GSW reels off 2-3 straight easy championships. They already tried to help the small market teams with the max player rules (but it backfired) so there is some precedent.
The tough question is what do you do if you have a superstar in their prime and are good but not great, like SA and Houston. Playing for a WCF appearance is a tough sell to fans and superstars alike.
We are going to either see a ton of rebuilding to be positioned once GSW implodes or more superteams will be formed to try to challenge.
The worst thing for the NBA would be the warriors winning these final in 4 or 5 games and it looking like no end is in sight. As long as the LeBron's are posing a tangible challenge then I think the NBA is content.