Well since the majority of Bill’s net worth is probably in Microsoft Stock. He would have to sell the stock to either current employees or on the open market. If he were to sell that many shares on the open market, the stock price would drop substantially. There would be too little demand for the supply. This would decrease his worth substantially. OTOH, assuming he could sell it and keep the price high, all it would take would be enough people wanting the stock and purchasing it through their brokers to give him the money. Since he would not likely keep the money sitting in the house, but would re-invest or put it in a savings account, the money would not really leave the money supply, just be moved around a bit.
Considering that the current price is around $86 per share, that would mean that Bill has about 1.16 Billion shares, if the $100 billion number is accurate. That would take 11 Million people purchasing 100 shares each. Not that many in my opinion. Especially, if you add in various mutual funds and large investors.
Also, considering that last I heard, there is over $1 Trillion in 401Ks alone, and probably more in the stock market, it would definitely be doable.
Since the volume for today so far has been less than 10 Million or less than 1% of Bill’s shares, if he were to sell them the the price would likely drop from 86 to almost nothing, since why would Bill sell, if there was not a major problem, then everyone would sell. It could become a penny stock and he might not have much at all. You might even be able to purchase all his stock yourself.
Could be done, but would not be wise.