Curious ability. It'll be rare for it to matter: dying in combat will be too late for flying to matter, and even in the case of sorcery speed kill spells you'll only benefit if you left this back to block and another creature of relevant size as well.

Put it this way: I'd pretty much always have Aven Fisher.

Maybe this was a set up for a card with the Essentia mechanic?

As Alex correctly pointed out the use is still very narrow - and if this really wants to interest you in using this card with essentia, then the benefit should be more cost-efficient e. g. this could be easily and the narrow death trigger would feel better as a reward, because you got access to it sacrificing a cheaper creature - which makes the card more usuable by itself and is something better flowing into essentia (you don't want to sacrifice your expensive creature to get your spells cheaper, you sacrifice trash).

I'd argue even better would be to put this ability on a cheap non-flier, that you maybe have in your deck to provide an early blocker, but can later in the game combine with essentia to get through a blocker.

It's a more pronounced reward than giving a permanently evasive creature to hand out temporary evasion (even if sometimes you might have that large creature to finish off an opponent with a single evasive attack).