When someone jumps on you and yanks you to the ground before you even know it, then how will your aikido help you then?
FWIW, Here is an interesting piece of semi-formal research on the whole "95% of fights go to the ground" thing.
I think I originally found this link somewhere on these forums.
The findings of this survey are that less than half of fights go to the ground, and when they do, the person who is on the ground first is usually the loser. I would therefore expect my Aikido to help out quite a bit if somebody tried to pull guard on me in a rules-free context.