Tony Stark is alive.
It was on Reddit but the thought is that Tony Stark put himself into an computer type program. Think Ultron. Think Jarvis. Maybe in the five years Tony Stark put his intelligence into a holographic type (Obi-Wan) being. The thought came from the end of Endgame as he was making eye-contact with the people in the room while, seemingly, making eye-contact with his daughter Morgan even though the hologram had been "taped" much earlier. Apparently there is precedence in the comics as well. Or, think of his dad's statements about how he, Howard, was prevented from making the new element due to his time... the technology hadn't been invented yet. Maybe Peter, or Morgan, break through new technology to see/bring back Tony Stark's consciousness... or maybe it will be the Fantastic Four... or Professor X.
This would be one hell of a surprise in the next Spider-Man movie or something when Peter boots up some Stark technology and RDJ's voice begins talking to him.