it's not dead.. so it'll keep growing. May be delayed a bit compared to any others planted at same time.
It's a bit scary, but get that shell off ASAP, next time. A pair of small tweezers to secure the shell -- make sure it's only squeezing on 1/2 of slightly split shell. then either a toothpick or another pair of small tweezers to pry and gently split the shell further. Hold the whole thing steady as you work it, so you put little to no stress on stem and roots. There may be a membrane behind.. don't try to take it off like the shell.. this memebrane can be slid off. Gently poke toothpick between leaves at base and gently slide the membrane off.
Easy peasy.. once in a while you will rip a cotyledon off or maybe worse.. becareful, take your time, and it's a rare occurence.
Bury it slightly deeper next time -- emphasis on slightly. Too deep and it delays the sprout needlessly. Shell-head should be rare, though.