Rooting hormone? It has a root system, it needs a new growth shoot. If it was a healthy seedling and there's enough energy stored in the roots, there's a good chance it'll attempt new growth. I've had several low grafts (below the first leaves/internodes) on seedlings that have failed; the seedlings have sent up new growth shoots more often than not.
I would keep the seedling on the same water schedule but avoid fertilizing it. If it's in a pot, move it somewhere it still gets sun but I'd avoid full sun (it no longer has any leaves shading the soil, might dry out fast on you). If you see several new growth shoots, leave the strongest shoot and remove the rest. If you don't see anything in ~2 months, I'd say it's a lost cause.
It's a good time of year; if it does recover, it'll have the chance the flush a few times.