Tooth crown

I had a root canal treatment because my tooth was in poor condition.

Currently, I have a temporary tooth.

They decided to do a crown, but since the condition of the tooth is poor, they said it can't be crowned.

We said we would do it when your condition improves, but is it possible for the previously problematic tooth to get better?

I'm wondering if the doctor was just saying that or if it's actually possible to improve later and reach a state where it can be used.