A Very Long Time™ in miles? Erm, probably about twice around the Earth, riding through oceans included.
THe bearings can be replaced and the hub can be overhauled: the chap in that thread I linked to who gave the bearing info has had his down to its component parts and back again – therefore the hub can last forever, hurrah!
A SA and front mech setup would indeed be LOTS cheaper but wouldn't have even half the gear range of a Rohloff. I've tried an Alfine with a front mech but unless you have massively different chainrings the range is still limited.
PLUS I hate front mechs so are one of my favourite reasons for having hub gears instead.