If they wish to sell the game at a retail price I would highly recommend for those that play offline to have a full beginning and ending.
However I do know the story will be on going so may I recommend staying away from the “To be continued” cliff hanger that tries to force players to get an online pass? Okay hear me out.
Typically in action series the heroes take on a huge plot to kick things off, Like while Overwatch was gone Talon and or Null sector had been planning something big something that took years to build up, The heroes uncover this plan and goes through missions to stop it, there’s a huge final boss fight and the world conquering machine the important to the plot item is either recovered or destroyed, the villains are back to square one and Overwatch is declared as heroes, the end of that plot.
But the while their decade long plan is gone for good, the villains are still very much active and have way more plans and Overwatch will be there to stop it.
And THAT’S where the passes will come, Each season pass can contain episodes which consist of a series of missions while the typical OW rewards (Skins, Emotes, Sprays etc)
All missions can downloaded to be played offline.
Or course any and all cosmetics can be taken to PVP.
Soooo whatcha think? A nice fully loaded story to possibly have players wanting to see more action and adventures with the heroes and still keep the “Live service” but players get something to keep.