Yes. It may not seem it, but that scooter blenny actually needs to feed on microfauna in order to survive. This means you need to have that lil tank PACKED with lr, and it needs to be well established. If not, then Id bring the lil guy back for another type of blenny. Maybe a sailfin blenny or one of those purply ones. Scooters and those red ones are members of the dragonet family, meaning that they feed mainly on microfauna and pods. Without this food, they will slowly starve. Every now and then, there is a phenomenon in which a meber of the dragonet family will eat brine shrimp and other frozen foods, but this is rare. And the damsel? I dont think you can kill a damsel as long as u have sufficient food (any kind will do) plus okay water temp/ water levels and temperature. Well, please, let me know how much rock you have in there. If not enough, I would either suggest setting up a refugium and packing THAT with live rock, THEN adding a scooter in the future, maybe even a mandarin, or for now, just bring that cute bugger back for another. I bet the lfs didnt tell you or even KNOW the food requirements of scooters....