Yes he should pay for the repair or replace. Another thing that might be a problem, is the "mastic". It should be thinset, as mastic is not suitable for wet conditions such as a tub or shower situation.

absolutely. our contractor chipped ours too and he had it repaired - we asked him to guarantee the repair and he agreed.

The electrical contractor replaced my tub after someone dropped a tool on it and chipped it.

Ironically I am tearing out another bathroom and it took an entire section of tiled wall with mortar and wire mesh (a 6 x 3 foot piece) that weighed a ton to finally chip the cheap steel tub I am removing. I was throwing broken tile, dropping the crowbar, all sorts of stuff and nothing. But sneeze on something you are Installing, and of course it gets damaged.