What if Mohammed Zahir Shah was never deposed? The king was pretty liberal, tried to modernize the country. Sure he had opposition from the conservatives, the Communists, the Pashtun nationalists, but it seems to me none were strong enough to oust him until his idiot cousin launched a coup.
Zahir Shah lived to 92 and died in 2007. Afghanistan could have had decades of peace under an open minded monarch who ruled with a fairly light hand. Was this likely, or was Afghanistan doomed somehow.