Instead of ending up back on our world, he ends up somewhere else. A different flavor of magical land. The moon was in the wrong phase.
So now he has to go through all of this again, but less prepared and without a guide this time. But he knows some basic magic now, so that helps a little!
This fantasy land is much 'higher magic' than the previous one, and after he gets dragged before someone important they give him a magic necklace that translates for him. Which helps speed things up a lot, but its expensive and if he wants to keep it he'll have to pay off the debt.
Interestingly, while this new world has more common magic than the last realm, it shares almost nothing in common with what he was taught. The basic magic shit he has only barely learned and was a novice at in the prior world is, here, totally unheard of.
This sets the theme for future arcs. Each arc is a different world, the language barrier glossed over by the necklace from now on. In each world he goes to he learns some trick or acquires some tool that is unique to that place. He never masters anything, but he eventually ends up with a combination of tricks that were never supposed to go together, exploiting combos that other people can't because they haven't been the places he has.
He just wants to find a way back home, or as things get worse at least find a way back to a world where he has friends.
By the time he finally makes it back to earth its been 20 years and he is rolling is power armor with magic items he has built into it or strapped on top, with an increasingly absurd history of shit like fighting aliens or overthrowing ancient godkings. After all of that he is finally home.
The last arc is him trying to find his place in a world that has passed him by, and in many ways he has himself outgrown. He thought he wanted to go home, but is this even home anymore? No one believes he is who he says he is, and he doesn't even know if he should tell everyone magic is real.