On that subject - when Warren's stock holdings are charitably contributed at some point after his passing, what is the likelihood that the shares will be sold in large volumes over a relatively short period of time?

If this occurred, and given how large his stake is in Berkshire, I would expect a massive liquidation of shares to have a significant downward pressure Berkshire stock prices. But I wonder how long the effects of that could persist.

Here is what Buffett said in the 2019 letter to shareholders:

"Today, my will specifically directs its executors ' as well as the trustees who will succeed them in administering my estate after the will is closed ' not to sell any Berkshire shares. My will also absolves both the executors and the trustees from liability for maintaining what obviously will be an extreme concentration of assets.

The will goes on to instruct the executors ' and, in time, the trustees ' to each year convert a portion of my A shares into B shares and then distribute the Bs to various foundations. Those foundations will be required to deploy their grants promptly. In all, I estimate that it will take 12 to 15 years for the entirety of the Berkshire shares I hold at my death to move into the market."

Berkshire Hathaway: PDF document

Similar distributions have been going on for quite some time with Buffett's annual donations to the Gates Foundation. The Gates Foundation has been selling 5M or more B shares per quarter in many, if not most, quarters for more than a decade. See dataroma.com - M activity.

So, I don't worry too much about a "massive liquidation of shares" after Buffett passes.