Has anyone calculated the compounded annual return for Berkshire from here under the following cannibal conditions?

It depends on the valuation level at which buybacks are done. If done on average at fair value, the value of a remaining share axiomatically doesn't change.

Speaking purely for illustration, if the firm is currently valued at book for cash and investments, but at X times earnings for the rest, the mix of those two would change but the total wouldn't.

So, to a first approximation, the trajectories of value and price would be unchanged in a cannibal scenario.

It depends a bit on the multiple you think the cash pile is being given by the market. Face value? A pinch more because Berkshire has always managed to find a profitable way to deploy it before too long? Or lower, because the average market participant expects some of it to be wasted? (paid out triggering high dividend tax, earn nothing for too many years before being allocated in an average way, dumb capital allocation by the new boss, whatever)

Overall I don't think it would make a big difference. Which leaves the question of what the owner earnings are now. Maybe just look at the median rolling year rise in book recently?

Biggest recent wildcard isn't the cash pile, but the big permanent hit to the true value of BHE. Unquantified but immense.

Jim