And then Norman Osborn appears in Peter's life, post-IW and post-Tony as the MCU Scar...
But in all seriousness, that comparison
does make a lot of sense and I could definitely see Tony sacrificing himself to save Peter in either Infinity War or Avengers 4.
As for Tony and Pepper getting married, I feel like that will either happen at the start of IW or at the end of Avengers 4. It all depends on whether or not Marvel wants to kill Tony off- if they do, then have the wedding early on so that it's all downhill from there for Tony. If they want him to live, then save the wedding for the end of A4 to act as Tony's "riding off into the sunset" moment in the MCU.