This honestly seems like the author of this manga wanted to appease both sets of fans for which ending would happen. They both die as to go with the ones who wanted a more tragic end, but at the same time the two end up together for eternity in their own world to appease the people who wanted a happy end.
I am one of the ones who wanted a happy ending, so I shall make the cannon ending them managing to run away and actually start a happy life together. Is it a cop out? Yes, but I wanted them to be happy, which granted they are, but I wanted an ending in which they LIVED a happy life first.
I just woke up, I didn't need this depressing stuff to be the first thing I read. Now, if you'll excuse me, I'm going to forget this tragedy with Vtuber Yuri and cute anime clips.