Obviously, since Guardian is a cyborg, basically, he can be 'rejuvenated' and live again as Guardian, maybe with less engineering acumen but more heroism and such. Heather as Nemesis, since it's a cool role and Mistress of Fate is better than being just dead. Puck may have residual immortal magic.
Of course, depowered Flex or Radius could be Guardian, with interesting twists for other characters.
I wonder how many proposals Marvel has gotten for Flight this time around? I'm betting around 3 per month.