I wouldn't hold my breathe if anything you could dip it in root gel to see if it might do something but tap roots that break often die 98% of the timeI did this once and just pushed that little stem down in the soil. It eventually rooted itself but of course was weeks behind the others in growth. I topped her once and she grew out to the the same height as all her siblings, but they were mainlined and lst'd, so 4 times the size of her. If it's an important seed to you, give her a shot. She may surprise you.
It does look like it's already done for, but i'd be patient.
Contrary to popular opinion the tap root isn't essential to bud growth, plants grown from cuttings don't have a traditional tap root yet they still produce large plants which are genetically identical to the mother plant. It may just slow down the process...good luck
I was just stating that the possibility of this girl pulling through exists, if the seed is important enough to bother with. I never expected it to survive, and so didn't do anything special, not even rooting hormone. Just FFOF soil and ph'd water. She was no longer than 3/4" when she broke, had cotyledons and the first single blade leaves were just starting to poke out. I stuck her back in, and watered and made sure the top of the soil didn't dry out which wasn't hard with a mini solo cup and a 26w cfl.I wouldn't hold my breathe if anything you could dip it in root gel to see if it might do something but tap roots that break often die 98% of the time