Responses
You are correct. This is the part where many manga readers got confused with. They only showed it visually, not even including a note like having a dark blank page with a quote by Eren saying “I’m glad I lived the four years I had with Mikasa” then show the whole thing playout and could have told Mikasa that he was going to return back in time to hint the readers on why that scene was there. Since we already know the founder has the ability to manipulate time.
i saw a tiktok where they said that time in paths and in real world are separate, and in ch 138 the vision starts when eren has 4 yrs left to live and ends with him dying from the titan’s curse. which means the vision lasted four years in paths. so technically, eren and mikasa still got to live four years together, but in paths.