That's one opinion. Often the head gasket leaks coolant into the oil only because the head is not torqued down as it started out, and leaky O rings are replaced anyway in a gasket change. I've rarely seen where a head was not straight enough to seal unless the engine was really cooked, more just that the head was not as tight on the block as it was intended. It never hurts to try the retorque first. I would worry more if the engine had been overheated to the extreme. Then yes, check the head for flatness.
Yes, there might be additional problems, would never deny that, but do the simple stuff first. We once did have a 2 liter head which leaked coolant. Turned out there was an open pore in the head, allowing coolant to leak into an exhaust passage downstream. That had to be welded up, but that was a very rare failure. However, changing the head gasket was the only way we found that out, as it did not change the situation. Head gasket kits are just not expensive in comparison to a full Monty job.
We still haven't heard why the owner thinks the head gasket should be changed.
1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6