At this point, there's no backing out unless you really want to demoralize the Kurds and Iraqi forces, enabling ISIS to continue to grow. Airpower has proven to be an effective force multiplier for the Kurds and Iraqi forces. Perhaps help the Kurds start developing their own organic air force and then eventually back out? But the question is, does the US trust the Kurds? And so far, does ISIS field anything dangerous to air power? If not, would supplying Kurds with simpler jet fighters suffice? Non-US fighters to avoid falling into the wrong hands?