Yes we know Warren won't "use up all the cash" and he has said so explicitly. One of the nice aspects of landing a large elephant is that at a company like Berkshire and the usual required time to close a large acquisition, tens of billions of dollars will be generated just through operations. Add in some sales out of the equity portfolio (remember we sold the other railroad stocks and that partially funded BNSF for example), BRK corporate bond issuance, shorter term borrowing from the next couple years type borrowing, and you can come up with a very large number even if BRK stock is not part of the consideration. If BRK shares are reasonably valued at the time and the merger partner insists on a small equity option, the buying power gets even larger.

A big reason BRK will not "use up all the cash" is that a large chunk of the "cash" is actually the bond portfolio inside the insurance companies. Berkshire is unique that their bond portfolio is so short in duration that almost all of it is classified as "cash equivalents," "t-bills" and "damn-near t-bills, wait a couple months" on the balance sheet.

But Charlie's point on buying power for the right deal stands - Berkshire has access to the money to pay for an acquisition if opportunity knocks. Charlie doesn't believe in taking a small plate to the pie counter when you get that invite.