Re: Downey's last?
Obviously this would never happen, but I've always thought it would be cool to have the avengers take on kang and introduce iron lad(probably could be a different name and a little older in the mcu) and then either stark dies, or retires and iron lad would take the place of iron man (taking up the name iron man obv.) and continuing the iron man legacy in the present time.
bottom line though, I can only hope rdj sticks as stark for as long as possible.
"Well, I guess the laws of physics cease to exist on top of your stove!"