I agree. Let the installer look at it. If you are wanting evidence to either convince the installer he is liable for the repairs and new cabinets or to take him to court, you are going to need a granite countertop expert opinion either way. We can't do that over the internet. Our posts would be inadmissable as evidence at trial. Who knows but your installer may be the resident expert in the area.
Does the person who told you that you would need new cabinets have any expertise? If anything, the installer probably used some caulk or adhesive caulk in a few places or even if construction glue was used, it can be cut free without ruining the cabinets. Usually the heavier the top, the less is used to tie it down.