What's the newest data analysis and results? --- EGR clean prevents HG gasket or is it inevitable

unfortunately, there is no data. data requires controlled testing and record keeping, of which we have none.
what we do have is a lot of experiences reported, good and bad. we do know that not every head gasket blows, if you put some mileage/time on the answer.

toyota says it is badly designed water pump speed software, for which they offer an update (in europe only?)
many guesses here include egr and related assemblies, defective head gaskets, 10k oil changes, infrequent coolant changes or even ph testing, poorly designed pistons and rings, and etc.
how to make sense of all that?

 

A lot of the naysayers give examples, owners that clean their EGR when the odometer's into six digits, and maybe even exhibiting head gasket failure symtoms, such as cold-start shakes, losing coolant. The concept of "interference engines" comes to mind, basically something advantagious is applied to an engine, with the caveat that something else is implemented, to allow that application to work safely.

With 3rd gen Prius, better mpg (a tenth or two of a mpg) was achieved, by running it leaner, and to keep the engine from overheating the EGR system was added. If Toyota had bothered to run a few test cars for 200k miles, we likely wouldn't be where we are.

Same could be said for the low-friction piston rings. Anyway:

^ A lot of times the naysayers will say "I cleaned the EGR, and head gasket still blew". When asked at what miles, it's typically around, well, your miles. Bottom line, just from reports here, my take is it needs every 50k miles, or less. Any more than that, the EGR is compromised, has reduced flow, unbalanced flow and/or overheated flow. Likely all three.

Belated cleaning is still good to do, but definitely don't get complacent. Our third gen YouTube guru @NutzAboutBolts cleaned his EGR and intake manifold around 120k, and is now having head gasket failure, around 180~190.

See the top two links in my signature*, also see this workflow summary (just for the EGR side of it, not the intake manifold).

* on a phone turn it landscape to see signatures

Not sure if it's mentioned in any of the above links, but exclusively for the EGR cooler, I'd recommend a lye solution soak, for fast/thorough cleaning. It's stainless steel, impervious to lye, and really needs something strong, due to the internal radiator labyrinth. For everything else brake cleaner, brushes and rags will do. You definitely DO NOT want to or need to use lye on anything else. It will react with aluminum, non stainless steel.