I have been repairing for almost 50 years now. I've seen a number of them do that. Usually you'll see an added string retainer disc for the 'E' and 'A' strings. ALWAYS on old P-basses, and Telecaster basses with that headstock. I've never been asked to offer a solution to that. Usually, heat, opposing- clamped -in- a- fixture- pressure, and time... can straighten out warped wood. Being that that looks like it has occurred over a long period of time, that warp may never come out. My experience with wood, is once it warps- in a single piece like that neck, it's where it WANTS to stay. I've seen this with 'S' curved necks, the fibers compress, and that's it. Warped necks with fingerboards can be straightened, but that, is under so much tension.... it's a good idea to just play it... until it becomes unplayable. For the record, of the ones I've seen, I never saw one that warped so badly it couldn't be played.