Agreed it has worked out for most people. However, it certainly possible for yeast to die and cause off flavors. Yeast health and the environment(ABV, pH, temperature,e etc) are huge factors affecting the chances of yeast death. Most likely you will be fine after 4 months, but to plan on leaving the beer on the yeast that long without good reason is inviting trouble. IMHO anyway...
I'd be more worried about the coming zombipocalypes then actually having it happen these days.
When yeast autloyze, the yeast cells rupture, much like we do if we develop peritonitis and our intestines rupture. Think the monster that bursts out of the guy's stomach in the original Aliens.
But as Palmer and Jamil have said it is a RARE occurance these days that yeast actually dies anymore,
let alone actually autolyses. It just goes dormant when the job is done and waits for the next round of sugar (much like when we pitch on top of the old yeast cake- which even some commercial brewers do for multiple generations.) The cells rarely rupture and die off.
Yeast ARE cannibals, but that's not a bad thing at all. In fact it is quite common to put old yeast, bread yeast, or "yeast hulls" into the boil, or into the fermenter to help the yeast, especially during high gravity brews. It works as an "appetite stimulant" to get them going.
It works really well for stuck fermentations.
You can buy "special" versions of this from any lhbs, but in reality dumping any old or new yeast into your boil kettle works just as well.
From BYO Magazine
Yeast hulls (sometimes called "yeast ghosts") are essentially yeast skeletons. They’re the freeze-dried empty shells of yeast cells that have had the water and other liquid elements sucked out of them. Sounds a little gruesome, but yeast hulls provide extra nutrients that are critical to a fermentation.
Thing to realize is Dead yeast and autolysed yeast ARE NOT the same thing. Not every dead yeast has it's "intestines" exploded, just like we humans don't all develop peritonitis. It's rare in humans, and it's also rare these days, since yeast is much healthier to begin with. It's not like 30 years ago (when most of those opinions that you espouse about autolysis originated from) when our hobby was still illegal, and there wasn't a lot of yeast available to us. The yeast used in hobby brewing was usually in cake form, which came from Germany and England in hot cargo ships and may have sat on a store shelf for a long time....or the brewer just used bread yeast.
Palmer even said this in the broadcast I quote from above-
So the whole health and vitality of yeast was different back then compared to know. Back then it made sense. You had weaker yeast that had finished fermentation that were more susceptible to autolysis and breaking down. Now that is not the case. The bar of homebrewing has risen to where we are able to make beer that has the same robustness as professional beer. We've gotten our techniques and understanding of what makes a good fermentation up to that level, so you don't need to transfer the beer off the yeast to avoid autolysis like we used to recommend.
Yeast in the 21st century is much healthier to begin with, and is less prone to have issues like their cells autolysing....just like our own health tends to be better these days.
It's so rare that you really don't need to worry about it....Even John Palmer has backed away from talking about it. All talking about it these days does is scare the noobs....
This topic has pretty much been done to death there.
https://www.homebrewtalk.com/f163/secondary-not-john-palmer-jamil-zainasheff-weigh-176837/
