They aren't leaving, but the Flyers could make Edmonton sweat in McDavid's UFA year, if Danny so chose. We have way too much money locked up through Drai's FA year, but by McDavid's, presuming only short-term contracts between now and then, our only commitments for the 26-27 year:
Couturier - $7.75M through 29-30
Farabee - $5M through 27-28
Sanheim - $6.25M through 30-31
Ristolainen - $5.1M through 26-27
Ellis (have I mentioned recently that I hate Chuck Fletcher?) - $6.25M through 26-27
We can expect new deals for Tippett, Brink, Cates, Foerster, York, Zamula, either Hart or Ersson, looking at Gauthier, Andrae, probably Attard and Bonk, of the kids, so there will be some young, developing talent there, but they'll all be on ELC or similarly early deals, so not taking up large chunks of cap.
Obviously there will be deals signed between now and then, but at the moment, the Flyers could add McDavid for whatever he demands, with an ELC Michkov on his wing.