Bathroom fitters chipped new bath! WWSTWD?

As part of a bathroom/shower room gang we’d replace the bath and would have sacked the plasterer straight away from your description of him as it’s up to the plasterer to sort his shit out and do a good job, the contractors sound rubbish.

I very much doubt a repair will be as tough as the original finish.

You asking them to either replace the bath or repair and compensate for the full value of the bath is exactly the right thing to do.