Islam owns atheism with a single verse

[Angrboda]

God as traditionally defined ™ is a necessary being, a being that cannot fail to exist.  

God as traditionally defined may or may not be a necessary being. The concepts of necessity and contingency are completely absent in all the major scriptures of the world religions. For all we know, the account of God in Islam may actually be that of a maximally great being, but not a necessary one, just enough power and "greatness" to make creating the world possible.

And it's worth noting that the only theistic arguments where necessity matters are ontological arguments, which are of dubious validity.

No. Necessity matters in terms of arguments about morals as well. As well as any presuppositionalist notions about logic, math, and rationality. (Though these may be ontological in the broad as opposed to the narrow sense.)