If the matter becomes reality how will the value of Bitcoin?
The scenario is so imaginary and it most probably is not going to happen, because first there are 195 countries in the whole world, some are small and some are big, but the point is, there are not 100 countries that can buy 100K BTC. Due to many factors, one the country would be a developing one with a lack of resources, second, illegal and law barriers. The point is 10 million BTC sale is almost impossible. Your whole question is so unexpected and based on personal thinking (biased one) plus it doesn't have any solid proves to back your theory up.
Satoshi first planned to sell 1000 BTC to Warren Buffet but for some unexpected event's occurrence Warrant Buffet has missed the Bitcoin game.
Where did you read this story, as till now I have not heard this before, you are the first person saying this. I suggest you to add the source link also so we can verify the validity of your statement. On searching I did find nothing on this deal you are talking about.