ᐅ IKEA Hällviken Undermount Sink Cracked

The problem doesn’t seem to be new.
Are there any suggestions on how to remove the old sink without damaging the granite countertop?
In theory, I could cut out the old sink and install a suitable drop-in sink.
It just wouldn’t be an undermount version anymore.

Assuming the entire kitchen is from Ikea and the sink is mounted in a base cabinet, I would rather saw through the cabinet and then install the new sink using appropriate attachment parts, or simply replace the whole cabinet. Without feet, the new cabinet with the sink already installed can be fitted in place. Then, lift it with mounting pads, screw it in from the sides, and finally attach and adjust the feet.

Thank you, I understand that. The issue is that the sink is not attached to the cabinet, but to the countertop, and it is glued.

Yes, the sink will have to be completely destroyed; there is probably no way around it.
Using a multi-tool with the right attachment and proceeding very carefully might work.
Chemical methods might also be possible, but I am not familiar with that, and you would need to know the exact composition of the adhesive.