Agents of S.H.I.E.L.D. ended its fifth season on a bit of a downer due to the deaths of three significant characters. Admittedly, Coulson was only dying at the end of the episode, and Dead Fitz is probably going to be replaced by Frozen Fitz after Simmons and Co. pull him out of his slumber in deep space, but Graviton seemed quite definitively dead after being blasted into space by Daisy. He was last seen floating lifeless in space, looking very, very, very dead. According to S.H.I.E.L.D. executive producer Jed Whedon, however, that may not be the case. When asked by somebody who loved actor Adrian Pasdar as Graviton if he could come back, Whedon said this:
This is Marvel, and even more, it's Agents of S.H.I.E.L.D. I know we see him floating in space, but he's Graviton, so you never know. So if the rest of the fans feel the way you do, then chances are he might not be super dead,
Death simply isn't always forever on Agents of S.H.I.E.L.D. This is a show that has managed to pull fake-out deaths on regular characters with no powers whatsoever; Graviton's powers aren't even entirely understood as of the end of the season, and the surviving agents probably won't waste too much time or energy on making sure that he's really dead in Season 6. After all, they're more than a little preoccupied at the end of the finale with saying goodbye to Coulson (and May, for a time) and getting ready for the mission to find Frozen Fitz. Jed Whedon's comment to EW definitely give reason to wonder.
For all the agents (and the audience) know at this point, Graviton may have just woken up shortly after seeming to die in space. Stranger things have happened on S.H.I.E.L.D. If the show could find ways to bring back versions of Grant Ward time and time again, surely the show can find a logical way to bring back Adrian Pasdar as Graviton if the producers are so inclined.
That said, Graviton is such a powerful bad guy that S.H.I.E.L.D. may not be able to bring him back into the MCU without causing some continuity issues between the show and the movies. The fact that Avengers: Infinity War didn't really impact S.H.I.E.L.D. Season 5 was already a stretch; Graviton coming back without catching the attention of any Avengers might be hard to buy. Now, if S.H.I.E.L.D. goes ahead and splits from the MCU, that would be a different story.
Whether or not Graviton returns to Agents of S.H.I.E.L.D. remains to be seen; the bad news is that fans will be waiting quite a while to see any of the characters back in action unless one of them scores a surprise cameo in another Marvel property. Season 6 of Agents of S.H.I.E.L.D. won't premiere until the summer of 2019. Coulson will appear in Captain Marvel, but not in the present setting. Fans may be waiting for more than a full year to discover what happens next.