Betta's tails and fins do grow back, it just takes a little bit of time.
4 Female bettas
Niblet, Melody, Valoo, Sephany
2 Male bettas
Head Trauma, Kyuubi
Buster, Tobias, Sinister
Phantom of the tank fish
Lisa Lopez, Frogger
Sorry, I am new to this site and still trying to figure it out. I chopped most of his tail off (this is embarrassing), but I chopped it off with a spoon. The long pretty part is gone, but he is still swimming.
That is very unfortunate, I hope he recovers. It is good that he can still swim. If he does end up having trouble swimming you can lower the water level to help him out.
The best way to help him recover more quickly is feeding him a diet high in protein (Frozen (NOT FREEZE DRIED) bloodworms/glassworms/brine shrimp) while keeping his tank extremely clean and warm to prevent secondary infection.
What size tank is he in? Is it heated? What is your water change schedule?
You can also use Stress Coat to help him regrow tissue.