All they have to do is add color commentary (post-game shows, direct interviews with players and coaches) and the value of local TV sports networks and intermediaries like ESPN will drop off to zero.
Only thing ESPN will have going for it is cross-sports content, like SportsCenter. Not sure that's enough to keep them going.
Once the cable and local network deals expire, the league streamers would be smart to do away with local blackouts, and then there would be no reason for fans to just buy the league streaming service directly.