> once you have that sort of money, there are only a couple of reasons to run it up any further:
Your reply seems to indicate you didn't read what he said, but instead read your own meaning into it. Your #3 doesn't make sense as a reason to "run it up any further".
In that case you shouldn't sell. The buyer might promise you everything, but once the deal is done, he will make his own calls, implement his own vision.
Microsoft can sell Mojang to EA the very next day if they want to.
3) you don't want the project to lose its integrity/vision. The dollar amount matters less than finding a fitting buyer at a good enough price.