Theists and atheists in foxholes are killed at exactly the same rate, despite the prayers of the theists.
Dead theists in foxholes are proof positive of the futility of prayer. Surely, given the dire nature of their predicament, the now-deceased theists prayed more sincerely and with more urgency than they ever prayed before. They were praying to a deity whom, they believed, had promised to grant them whatever they asked for in his name.
The remains of even a single dead theist would be enough to demonstrate that the promise was imaginary and prayer futile. Over the course of history, there have been tens of millions of dead theists at the bottom of foxholes. The god they prayed to is either non-existent or a liar.