There have been a lot of hints from David Harbour (who cannot keep his mouth shut) and others that Hopper is the American.

Plus, think of the other characters in ST who were thought to be dead but survived (Will and Eleven, probably Brenner too).

Will was never thought to be dead

He had a funeral

Yeah by the town not the kids

Right, Supernatural, but even Mike and the kids thought Will was dead - until they heard his voice on the radio. Go back and watch the last few minutes of the episode Holly Jolly and watch Mike's reaction to the finding of Will's body. Watch the first few minutes of the next episode (the Body) and note how much trouble Mike has convincing a skeptical Lucas that Will is really alive - - - the kids actually thought he was dead.

I know that I am just saying that was the shortest amount of time and joyce and el were the only ones who did not believe he was dead

Yeah but they would here him speak and from there they could obviously figure out that he was foreign, then from there an American

Yes but it does not prove he is alive