I did Kili last year and I only took my D700 and Tamron 28-70, I didn't miss any shots and believe me, you don't want to be lugging extra weight.
I'm pretty fit - I run half marathons for fun after a heavy Saturday night and even yesterday I did a 75 mile bike ride after an 8 hour session on cocktails the night before. So, I'm a glutton for punishment but even I certainly wouldn't have wanted to carry any more weight up Kili. Taking a 70-200 f/2.8 would be foolhardy and unnecessary IMHO, 6000m altitude is no joke.
Edit: actually, my avatar is me at the top during sunrise.
Also, no one tells you this but the dust is unreal, it gets everywhere! I would avoid changing lenses at all costs (and I'm not precious about my gear). If you feel you want more length than the standard zoom then I'd get a super zoom specifically for the trip, you won't need the f2.8 as the light is good as you're above the clouds for most of it.