It would need some serious scripting but if tit worked it could be quite cool. For example. Once a large base was created. NPC would need to be worked on from every aspect of a military base (or enough to make it realistic). Say the gun store chief, medics, MPs, chopper pilots, motor pool (think of Billko), Base chief and the likes.
And off the base. Civilians, Mafia, local police and if it was post war partisans from friendly to the US and some not so friendly. Missions could be accepted for different NPC for either money or for other reasons. Chopper pilots could be bribed to make drops in air drop that could not entered by trucks due to non friendly. Also if it was post war there would be ammo stashes from the partisans and Russians which could be found and exploited. Mafia contacts could be made for doing favours for them. Contract hit could be accepted as missions. Guns could be bought for the base store or of the back market.
I was also thinking about it being played in real time with an opinion for sleep.