There is still a lot of time between now and September as for the NFL that can be an eternity and they believe that things will be back to normal, somewhat. While alternative plans were likely discussed, they did not let the media in on those plans if they have them.
The bigger question here is how can they convince the fans to come back to football early in September? Or even August for training camp and pre-season games? This is something we simply don’t know enough about yet.
Obviously, Novel Corona-19 is the reason. As it stands right now, millions of people are out of work and within the next few weeks companies who agreed to pay their wages will hit the wall of that promise and will thus send more employees to the unemployment line.