How much does a front wheel last with disc brakes vs calipers?
It will heavily depend on the conditions, but it's not something you really have to worry about. 

At a rough estimate I have 25,000 km on my hybrid, with v brakes (there shouldn't be a huge amount of difference between rim brake types). I ride in all weathers, and much of the distance is commuting with some longer road rides and dirt tracks. There's plenty of wear left in the front rim, going by the groove that's there to indicate that, and most of my braking is at the front. This is an aluminium rim, and one built more for strength the lightness.