Oof, that is a bummer. But the coil is probably still usable, as what I would consider a B-class part.

For a service call or other instance where reputation is on the line, I wouldn't use it. Same for a high-use location or similar game. Or a restoration.

But for a game you're close to and can monitor, or situation where you're in a pinch, you might get lucky. It is still a functional part, you just need to be smart about and keep an eye on it.

Forceflow is right in that there really isn't a good way to bond the crack at the joint. But you might try laminating both sides with some thick, high-quality packing tape, or mylar. Something to keep the part from flopping around so easily. Vibrations may indeed cause it to wear free again over time, but it could hold a long while.

I have seen and worked with coils where the lug was entirely free of the bobbin (Gottlieb coils are notorious for this) so it's not the end of the world.

If the seller is replacing it, keep this one handy for an in-a-pinch spare.