I agree with both Galan and Mr Master.
The cross company politics is kind of what kills this, and the gems do seem to be indestructible..
However the very idea that the spear can even destroy a piece of god, leads me personally to believe it should be able to destroy one of the infinity gems or a wielder of them, provided it gets that chance. As I don't see them being higher on the chain than that.
However Thanos wielding the IG I beleive would win, as he could still destroy Superman.