Marvel Cinematic Universe fans are finally seeing Avengers: Endgame after a long one-year wait. Infinity War shocked audiences as Thanos achieved his goal and Decimated half of the universe with a simple snap of his fingers and the Infinity Gauntlet. MCU fans watched as some of the most beloved comic book heroes of all time turned to dust, presumably never to return. While it was shocking, Avengers: Endgame has taken it to a new level. With that being said, there may be one way a deceased character from the movie can come back. There are MAJOR SPOILERS for Avengers: Endgame below, so read at your own risk.
Earth's Mightiest Heroes are able to kill Thanos twice in Avengers: Endgame, but it came with a mighty big price. In order to kill the Mad Titan for the second, and hopefully final time, Tony Stark had to wield the Infinity Stones and snap his fingers to Decimate Thanos and his army. After seeing the damage done to Thanos and Hulk after the Infinity Stones, it was easy to see human Stark go down and ultimately die as a result. However, all might not be lost.
At the conclusion of Avengers: Endgame, before Tony Stark's funeral, we see the character in holograph form from an Iron Man helmet projection. He is speaking to Pepper Potts, his daughter Morgan, Happy Hogan, and Rhodey. He's cracking jokes and delivering a heartwarming message to his daughter. The same technology was used earlier in Endgame as Natasha Romanoff is talking to Rocket, Nebula, Okoye, Rhodey, and Captain Marvel from different areas of the universe, which looks similar to Stark's B.A.R.F. tech from Civil War. The hologram tech is taken to the next level in another Endgame scene where Stark protects himself and Hawkeye with a hard-light hologram shield.
This hologram technology of Tony Stark's may be the key to the character showing up in the future of the MCU in A.I. form. This is not unprecedented. In 2015, Marvel Comics presented a story by writer Brian Michael Bendis, which introduced the A.I. version of Stark while he was in a coma. The Invincible Iron Man Vol. 2 #7 introduced Riri Williams, aka Ironheart, who was brought on to continue the Iron Man legacy after building her own super armor and catching the attention of A.I. Stark. One could easily see Robert Downey Jr. showing up at some point down the line in the MCU as A.I., though it could cheapen Stark's on screen death.
As for Riri Williams, one could also see Ironheart showing up in the MCU. Carol Danvers is reportedly taking on the Tony Stark-like role in the upcoming Phase 4, but Stark may still be around, or at the very least A.I. bearing his personality. Robert Downey Jr. as a version of JARVIS or FRIDAY could be something MCU fans want to see down the line and it could keep RDJ involved in a limited capacity. Inverse was the first to bring up this interesting Avengers: Endgame theory.