The inevitable writing is on the wall for "Iron Man 4." We will see the movie, the only question is "When?" But after "Avengers: Age of Ultron" do we need to answer the question "Who?"

Marvel has often tried to sell the concept of a Tony Stark recast, that the franchise and the character is bigger than the actor-that nothing is permanent in the movie industry.

There were already rumblings of Robert Downey not returning for "Iron Man 4" and there is already speculation on his replacement. But it is already common knowledge that he will be around until "Avengers 3."

But what if even that is not set in stone? Various spoilers and teasers have been floating around. A recent statement by RDJ on EW:

"What you said about abdication is apt, but I think it's also about recognizing limitations. The downside of self-sacrifice is that if you make it back, you've been out there on the spit and you've been turned a couple times and you feel a little burned and traumatized."

Limitations that RDJ has consistently mentioned. A Moviepilot feature stated the uncertainty that most Iron Man fans have tried to deny:

"Downey also finished filming his part in Age of Ultron several weeks ago (much earlier than most of the cast) and referred to himself as 'unemployed', which has caused some online to suspect that Tony Stark may even be killed off in the movie.

While we consider this unlikely when the character is so lucrative, yet with no Iron Man 4 in sight, it seems quite possible that Downey will throw in the towel with this movie, as by the time The Avengers 3 starts filming, he will likely be 52 or 53."

Ultron was actually Stark's 'retirement plan' from active duty-"active" defined as physically wearing the armor. However, that plan goes haywire, as we may safely conclude. How does this affect Tony Stark-will the guilt drive him to a more 'permanent retirement' or even death?

Yet another reason to mark May 1, 2015 on our calendars. If our greatest fear turns real, then who will don the armor next?