actually, the timeline where link dies does happen. it isnt a “what if” scenario. its really complicated to explain, but basically, becuase of the wibbly wobbly timey wimey effects of time travel, link dies due to the fact that when he got back he never took the master sword (he was sent back to a time before he took it). and since he did not take the pendants (the three trials that are necessary for every hero to take the mastersword, again more explaination than i can give in a short explaination). therefore, there is a bit of a paradox in the adult timeline, becuase link technicly should not have the master sword at all now that he never touched it. so he dies, and thus we have a defeated timeline.