Some thoughs on the subject.
There are some category of Leica owners:
1) Those who love photography and want to have the best rangefinder.
Typically these are users. Most use second hand equipment, and a large part will have in-house development kits.
2) Those who love the image/fame of the camera and have enough money.
Typically these buy the new models (Camera and lenses) and use them little and have a nice place to put them on display.
3) Collectors. These are persons with a lot of money that collect for collecting sake and will have one or two cameras that they actually use.
Now to your question, what will these do when the digital M appears.
The first group, will not jump on it directly because of the price. They will write about it (on this forum), dream about it but not directly buy one. Most will wait for them to appear used, and if they get one, they are unlikely to stop analog photography. If they have only 1 M-body they will stick to it. If they have more than one, they they may sell one, but only to raise the cash for the digital M. Those actually may want to sell their M6 or M7 because these have the highest valye.
The second group does not own a lot of m6's. They have traded them in for M7's or MP's when these came out. This group is likely to jump on the digital M's, but as said I doubt if they will release a lot of M6's.
The third group will not sell of M6's. It is the natrue of a collector to hold on to it.
So all in all, it is unlikely that there will be a massive bulk of m6's to flood the market if the digital M will come out. Most will come from the first group, but since these will not jump on it the release will be over a relatively large time frame.
I'd expect a flood of m7's and on the market (and are hoping for that 😀 ). This will bring the prices of used m7's down, which in turn may lower prices of M6's. But this will bot be by much. The current price difference is app. 500 USD, so even a hit in the M7 price by 300 USD (20%) will not affect the M6 price much.
mad_boy