MIMF

The neck on this guitar was damaged in shipping. Is there anything to do but replace the neck? The only thing I see is that due to the nature of the crack the tension of the strings might keep it from getting any worse. Is this a valid thought or just wishful thinking?
Looking at the pics more closely the low E side looks more like a dent than a crack. I don't know what that silver blob is under the nut. There is a shim under the nut that is visible here also. The guitar is in California and I am in New England.
Here are a couple better views.

That doesn't look like a crack to me. It looks like a tool mark of some kind, and it looks like someone did something to that nut in some way. It looks like a small nail or something jammed under it. If the wood was going to crack there, I don't think it would break against the grain like that.

I agree with Marks assessment on the bass side but the treble side looks more like a crack to me.
You could take the nut off and see what the bottom of the nut slot looks like, if it is a crack it should
be visible on the base of the slot.
Steve

Curious. It is difficult to tell definitively from a picture, without being able to roll it in the light and look at it from all angles, also to see if any finish is down into the suspect areas.

As Mark said, the bass side first looks like a tool mark but needs better inspection. Also like Mark said, the wood is not likely to brake directly across the grain, though anything can be possible. Usually necks break along the grain with some irregular cross grain fracturing.

You are correct that string tension will help keep the headstock in place.

My first inclination would be to take out the nut and the shim and have a look. But before you do so consider any guarantee implications. If it were a classical guitar when the nut is usually loose then it it would be no issue but here both the nut and the shim might be glued in.

There are no guarantee implications as I built this guitar. However the shim is glued in.