Much of the time the necessity of the northbridge fan depends on the cpu sink/fan.
If you have a massive cpu fan and the outlet of the cpu sink blows across the northbridge, good to go. Massive fan and it's blowing somewhere else, may, maybe not.
That's one downside to running an Alpha 8045 with a slow speed fan. It pulls air through instead of pushing which doesn't help the northbridge and it enters on all four sides which decreases flow in any one spot even more. Then top it with a slow fan and it's near useless to the northbridge. My nForce2 northbridge has a larger sink on it, no fan. Sitting near a 8045/panaflo it gets hot, uncomfortable to the touch hot. I have little doubt if it was a small sink meant to be paired with a fan and the fan died I'd need a new one or different sink. In brtspears2 case, pun intended, it didn't prove necessary.
Had this same sink/fan combo on my last board, a KK266-R with a KT133A. Board came with one of those dinky greens for the northbridge and when I originally had a FOP-32 on there it was always cool to the touch. When I switched to the 8045 it ran finger burning hot after, to the point I finally just ducted some air towards it when I started getting lockups during gaming/encoding.
Something to keep in mind for others who have fans (working or not) and are reading this thread out of curiousity.