Most worms can regenerate lost body parts as long as it's not too severe for them.

Though... if you continue to keep your worm bin, you'll face dead worms eventually. We all did. You'll have to get used to it, and try to not mind it too much and don't beat yourself up.

I lost few worms when they crawled into my bin's top edging and got stuck then died. My mom lost few worms when they escaped from drainage holes at her bin's bottom, and shrivelled in sun (though she did manage to rescue the remaining escaped worms and got them back in)

Just how it is.

Forgot to add:

Worms have nerve system so they're capable of feeling pain but in a different way than we do. When a worm twist or curl if you poke it, it doesn't mean the worm felt pain. It may mean the worm thought it's being grabbed by a bird so it twists to get free from a bird's mouth. Some people often misinterpret that.