IKEA Hällviken undermount sink is broken

The problem does not seem to be new. Are there any suggestions on how to remove the old sink without damaging the granite countertop? Theoretically, I can cut out the old sink and install a suitable drop-in sink. It just won't be an undermount version anymore.

Assuming that the entire kitchen is Ikea and the sink is installed in a base cabinet, I would rather saw the cabinet apart and then install the new sink with the appropriate fittings or replace the entire cabinet. Without feet, the new cabinet with the already installed sink could then be installed. Then lift it with mounting cushions and screw it in from the side, then put the feet underneath and adjust them.

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

Yes, the sink has to be completely destroyed, there is probably no way around it. With a multitool, the right attachment, and being very careful, it might also work. Chemically, it might be possible too, but I am not familiar with that and you would need to know the exact composition of the adhesive.