The plastic of the X-Wing minis melts like normal with standard polystyrene glue (I use Revell Contacta), so when allowed to properly melt and dry, it should be sufficiently strong to keep the wings on. they're not heavy at all, and there's no real tension, pressure or weight on the wings either, so it'll do.
I once snapped off the wings of a TIE Advanced because I wanted to convert it into a TIE Avenger. However, the shape of the hull would require so much work, I decided that it might be easier to just scratchbuild the thing, and I easily glued the wing panels back on with said glue.
That particular TIE has seen many dogfights since then, but it's as strong as ever...