If very high inflation does happen, what does that do to Berkshire?

An easy answer is that it probably raises the earnings on cash holdings, but that's not real value creation. It could arguably make future acquisitions (either common stock or outright acquisitions) more attractive to the extent that valuations decline as interest rates increase.

For me, the concern would be in any long-term contracts, particularly in the insurance subs. If we price policies based on inflation expectations that turn out to be too low, the future (inflated) claims will lead to painful results in those insurance subs. Probably easily manageable in annual renewals (e.g., auto), less so in other policies.

Of course, you can then argue there's a (maybe more important) macro effect where less secure or higher leveraged competitors are crushed by inflation and Berkshire ends up being the last man standing.

So ¯\_(ツ)_/¯