Guardians Of The Galaxy Vol 2: What Does The Ending Really Mean?
8. Nebula Is Baying For Thanos' Blood
It was widely reported that both Yondu and Nebula would be joining up to the Guardians team by the end of Vol 2, so it should come as a surprise that one of the ends up dead and the other strikes out on her own.
The fiery Luphomoid assassin reconciles with her sister by the end of the film, but declines to join the Guardians permanently, instead vowing to go after Thanos to make him pay for what he did to her as a child. She outright states that she is going to tear him limb from limb so he feels what she felt when he stripped her body parts away and replaced them to "make her better".
This could well be how the Guardians are drawn into the Infinity War story (besides a general guardianship of the galaxy, of course) - as Gamora goes to the aid of her sister (when she realises she's bitten off more than she can handle). And this may also be a hint that she could be the most valuable wildcard in Infinity War.
Without allegiance to the Avengers or the Guardians, Nebula can make a late appearance in the film, turning up to take down Thanos at the last minute - echoing her involvement in the comics arc. Whether she then ends up losing herself to the power of the Stones remains to be seen, but there are certainly hints in her fragility that she could.