How much would Warren Buffett and Bill Gates lose if they sold all of their shares in their main companies?

They would lose bundles upon bundles if this were to occur. But it won’t.

The main reason they would lose a lot is that the more of their holdings they sold, the cheaper each share would be, because there would be so much on the market. If there is no demand, you have to reduce the price.

So each one would steadily make less per share the longer the sale went on.

But it isn’t going to happen.

They sell off all the time. And normally on a schedule so the SEC doesn’t get all up in their shit. This is tracked. They report the schedule of the dates they will sell on. This is so it doesn’t look like they sell on bad news. See the Equifax guy.

Each of them could liquidate their holdings without disrupting the secondary market in their stocks.

They would do so through a negotiated placement with another entity, such as Gates selling his Microsoft stock to Jeff Bezos and Amazon.

Such transactions are not uncommon.

So to answer your question, neither would lose anything.

Gates is worth at least $90 BILLION and only 20% of that is in Microsoft. (Here is an outline of where is wealth is spread about.)

He gains billions per year from investments without selling anything.

What’s your definition of “much cash”???