I think its important to note that Luke's unique Jedi status has always been a misdirection and never what makes him uniquely capable of defeating the Empire.
I always found the idea that Luke was actually the last force user left in the whole galaxy to be beyond ridiculous. If Obi-Wan and Yoda could hide for that long, there's no reasons others couldn't do it as well. The only reason Obi-Wan was killed was because he confronted Vader on the DS.
Yoda was never found again and died of old age. So there's simply no way Luke could be the last force user out there. He could be the last classically trained and recognized as a Jedi by a Jedi Master. Because Kanan, Ashoka, Ezra, ect... They aren't Jedi. Neither is Vader or the Emperor, or Maul...
So there's no reason why any of the Rebel's cast needs to die, there will be no harm to continuity if they exist off camera. I also the idea that they need to die because they weren't seen in the other movies is again amazingly short sighted and looking for a fix for a non-existent problem. It's not like the movies represent 100% of everything that the Rebel Alliance does.