If you sell the bodies, keep one of the Nikkors and get an adapter to use it on the M9.
I'm considering selling my S2 and SP (both with 50mm f/1.4 Nikkors) to help fund a Leica M9.
I don't use them as often as I should, and I'm really in love with the M9 (you can read my review here: http://www.nikonweb.com/m9).
I know it's a stupid question, but I'll ask anyway. What would you do?
One thing is certain: if you sell your Nikon RFs to buy an M9, in a few years time the M9 will be worth less than it is now, and the Nikon RFs will be worth more.
Something to think about.
My guess is no matter how many photos you take with the M9, you'll regret selling the Nikons. Buy something like the d-lux4, use that for awhile nand see if you really need a M9 at $7,000 plus the expense of lenses.
You can't really bring depreiciation into it. The Nikons no longer pay their way, they are at the moment expensive, albeit pretty, bricks of metal. The M9 however will be paying its way, you can't put a price on the pictures it will be taking during said 5 year period.