I'm worried about dental treatmentㅠㅠ

Hello

Today I went to the dentist for a scaling, but I found out that the space between my molars was decayed and needed treatment, so I suddenly received treatment. However, I have to go back to work, so I only drilled the small molar and made a mold. But the large molar looks like it is heavily decayed in the X-ray, and they said they would remove the gold crown and carve out a lot, leaving very little of the remaining tooth, so I need to have the entire tooth restored.

Should I cut it down for treatment? I'm hesitant because it's a tooth... Is there a way to treat it simply without cutting as much as possible?