Is my seedling dead?

You kind of answered your own question there...If its dry, water it lol. May not perk backup though im afraid, but see how it goes.

 

Looks like it has a chance. If the roots are coming out of the rockwool then I'd say it will be fine. Just give it water. If the plant couldn't hold itself up or the leaves were drying I'd say it'd be less likely to live. I think it will be alright though. Just keep in mind seedlings need humidity and a moist soil medium because if they dry out when they're too young they don't always come back like a bigger plant normally would.