that's not registered, not roadworthy and has several issues eg dents from minor collision, issue with door handle etc.

Is it worth still trying to sell for a low price on FB Marketplace, Gumtree, Car Sales?

The car still works, it's an automatic sedan, it just needs a service to get back on the road. Without further info, what would you guess it'd be worth?

If you don't think it'd sell secondhand, what's a good wreckers that'd give a decent amount for the wreck/parts?

Maybe you should announce the car for a couple of days and be open to offers. This will give you an estimation of how much the car worths as is.