Happy Birthday, Warren!

The legendary Warren Buffett turns 94 next month — Aug. 30 to be exact. And as is frequently the case when he turns a year older, investors wonder what a post-Buffett Berkshire Hathaway will look like. That’s especially true this year, with Buffett’s longtime partner Charlie Munger having passed away last year and CEO-designate Greg Abel waiting in the wings.

I’m a Berkshire investor myself, and I don’t plan to go anywhere when Buffett is no longer part of the show. If you are a Berkshire shareholder, you might want to keep your powder dry as well.

Why? For one thing, Greg Abel seems unlikely to mess up the formula. And — ironically — because Berkshire’s days as a marvelous investment seem to be over, its astounding long-term record under Buffett notwithstanding. In many ways, Berkshire has become more like an index fund than a conventional corporation.

So it’s not as if something magical will depart when Buffett does.

According to Berkshire’s most recent annual report, the stock returned 4,384,748% to its investors from the time Buffett took control in 1965 through the end of last year. That’s 140 times the 31,223% return for the S&P 500 (^GSPC), the standard market benchmark.

But that was then, and this is now.

As I’ll show you, recent Berkshire investors — including my wife and me — haven’t done remotely as well relative to the rest of the market as Buffett and his early followers have done.

A little background is in order.

For most of my career, I didn't own Berkshire because I was an employee of publications that frequently wrote about Buffett. So I never bought any shares during Berkshire’s salad days, much as I wanted to.

But on Jan. 7, 2016, the first week that I became self-employed, my wife and I made a modest purchase of Berkshire stock in our joint brokerage account and have held it ever since.

And guess what? The huge long-term advantage that Berkshire shows compared with the S&P 500 has totally disappeared since our purchase. In fact, we’d have been a bit better off buying an S&P 500 index fund than buying Berkshire.

From our purchase date through last Monday, Berkshire was up a respectable 214%. That was also its total return because it didn’t pay any dividends during that period. However, during that same period, Admiral-class shares of Vanguard’s S&P 500 index fund returned 232%, including reinvested dividends, according to calculations that Jeff DeMaso, editor of the Independent Vanguard Adviser, did for me.

In other words, my wife and I got into Berkshire when its stock market glory days had passed.

And that — strange as it may seem — is a major reason that I’m not concerned with what Greg Abel will do at Berkshire when Buffett passes from the scene. Last December, shortly after the death of Charlie Munger, Buffett’s longtime partner in running Berkshire (and my longtime friend), I wrote that I saw no compelling reason for my wife and me to sell our Berkshire stock.

I still feel that way because there’s no reason to think that Abel will change the company drastically if he ends up running it when Buffett ceases to be involved. After all, Abel, who’s 62, has spent almost 25 years working for Berkshire, and Buffett named him his heir apparent three years ago. Abel seems to be a Buffetteer through and through.

In addition, you can make the case that Berkshire, which owns lots of different, unrelated US businesses, including big chunks of stock in Apple, Coca-Cola, and American Express and numerous other US and Japanese companies and batches of other assets, is sort of an index fund itself. (What's a more vanilla investment than that?)

Then there’s the tax question — which may or may not apply to you. My wife and I bought our Berkshire in a taxable account because I knew it was highly unlikely that the company would pay any dividends while Buffett was involved with it. So selling now would mean forking over more than 30% of our 200%-plus Berkshire profit to the IRS and our state government.

A final reason that I feel no compulsion to sell Berkshire just because of a likely management change is that companies' founders or longtime chief executives are often succeeded by competent replacements.

For example, Tim Cook has done a fine job since taking control of Apple (AAPL) from legendary co-founder Steve Jobs in 2011. And Walmart (WMT) didn’t blow up — and actually thrived over time — when the legendary Sam Walton died in 1992 and was succeeded by David Glass.

So, my inclination is to stick with Berkshire and see what happens if I outlast Buffett. And who knows? Should the stock drop sharply when Buffett passes from the scene, I may be tempted to buy some more of it.

Maya Benjamin contributed research to this story.

Allan Sloan, a contributor to Yahoo Finance, is a seven-time winner of the Loeb Award, business journalism’s highest honor.