God on the brink?

In a long excursus on John 3:16 and 2 Corinthians 5:19, Barth twice refers to God risking his "own existence as God" in the work of Christ on the Cross. He continues

"It is his self-revelation and self-realisation (in and for the world) as a gift, and rebus sic stantibus that can mean only the offering of that without which he cannot be God, and therefore of the greatest possible danger for himself."

I'm still trying to make sense of this!! But it seems odd that Barth, having absolutely insisted on the total freedom in which God carries out his redeeming work should now present God as driven by some inner necessity towards an act of (potential) self-destruction.

Can God cease to exist? Is he just another thing which can flash out of existence and leave everything else intact? That doesn't seem right - God is just more than one more thing in the universe. Or, if he exists at all, is his existence necessary in the manner of Anselm's ontological argument?