I can't choose. I think they would both be equally devastated.

Psychologically she would probably develop a dependency on him since he was the first person she met outside of her "mother"

According to Eugene, Rapunzel was the first person to like Eugene Fitzherbert more than Flynn Rider, so I think as a person with no family or close friends, he'd be super psychologically tied to her...

Also, he was willing to die in order for Rapunzel to be free. The concept of her being imprisoned was unthinkable to him; imagine how the concept of her dying would be.

Rapunzel would definitely be devastated if Eugene died, too, though.

I know we saw Rapunzel cry intensely over him, but I feel like after a while she would've left the tower and found her parents. I think if Flynn lost her, he'd be more broken because she was his new dream, and he does basically let himself die for her, so he probably wouldn't be okay for a while.

I picked Rapunzel at first, but these last two comments have convinced me otherwise.