The Principle of Contingent Causation: The Impossibility of Infinite Regress.

[polymath257]

Quantum foam seems to be noncontingent...it can't not exist.

Interesting point. I don't know anything about quantum foam.

Is there anything that must exist in order for quantum foam to exist? 

So by analogy: it's clear that hydrogen must exist for water to exist; if all the hydrogen suddenly disappeared, then water would disappear too. 

Is there anything for which we can say "If X disappeared, quantum foam would disappear too?"

Not that we know of.