I have a touch under 250k on my 4Runner, and it's been supercharged for every single mile, ever since 1999 as it was a dealer option. No drivability problems whatsoever, I finally pulled it off to send in for a rebuild preemptively as it wasn't really making odd noise and the nose cone spins very easily and quietly. Only issue is the O rings in the bypass tube stopped sealing and created a vacuum leak that was quickly fixed with some RTV.

Bump. I have a 98 with 280k that I'm itching to bolt on the new Magnuson TVS1320. Seems counterintuitive to bolt on a potential issue to a motor that has been so good over the years. But damn, I'm hungry!

I've been thinking the same for a while and tbh it's just not a good idea. When I was looking up some accounts of people supercharging around the 300k mark I found some guy that added one between 300-350k and it didn't even last a year before it blew his head gaskets
If you did head gaskets recently it might hold up a little better, but that also means the next weak link would be at risk, which would likely be piston rings or valvetrain. A compression test would give you a better idea on how strong those still are, but wouldn't tell you how much longer the trans will last from the major increase in hp/torque (don't forget a 7th injector is very commonly needed just to avoid pinging at lower elevations which would only boost the numbers higher)
People like to say "well you can always just take it off" but that doesn't do you very much good once the engine's been damaged or you've burnt up a gear in the trans
Ultimately it's your vehicle and your money but personally I find it to be extremely risky

How are we to arrive at the conclusion that the SC was the reason for his HG fail? At this mileage, it seems that is risk with or without.

Good call on the compression test though, maybe I'll start there as a general health checkup. I have a TRD second gen SC on my auto trans garage queen, and since I live at elevation I've never needed extra fuel mods or otherwise and never experienced pinging. This higher mileage mountain beater is a manual, so I'd like to think trans may hold up a bit better, though it is due for a clutch.

Will continue to ponder. It is a lot of $$ to throw into an old rig.

There isn't any outright definitive reason to know/discern it was; however blowing head gaskets with forced induction is extremely common due to increased pressure in the combustion chamber the heads+studs were never meant to see - which is heavily exacerbated by both old, tired gaskets and engines that were designed to be low compression, such as the 5VZ - not to mention radically increased temps which have a similar effect. Detonation doesn't help either. And while they're all meant to go sooner or later, with all that information in mind one could readily deduce (or at least make a reasonable assumption) that, at the very least, it was prematurely hastened along by adding a blower at such a late stage in it's life. For other examples you can look at nearly any NA engine that people turbocharge and attempt to run tons of boost through - head gaskets are most frequently the first to go