If you had a torn cv boot, it was a 4x4. The cv doesn't actually transmit any power when you're in 2 wheel drive mode. So unless you did many miles in 4x4 after the torn cv boot, you wouldn't really ever experience a problem with it. That's very different than a FWD car with a torn boot.

A CV boot keeps dirt from getting into the CV joint and keeps grease from flying out. Dirt that gets in causes increased wear.

Unless the boot is majorly damaged, very limited dirt gets in, most of the grease stays in, and lifetime of the joint isn't severely impacted.

The point is, yes his grease flew out. And dirt got in. But his CV joints aren't being used, they are just free spinning around all day not moving any torque. So yes his torn cv boot didn't give him trouble in a Toyota 4x4. It wouldn't have given him trouble in a dodge 4x4 either..

At some point I was expecting clicking or grinding, but it just kept going.

How long do unsealed CV joints usually last?

(At the time, I didn't have access to a garage, so it was more than I wanted to repair at home)

Yours will not/did not click or grind because it is not being used. You owned effectively a rear wheel drive truck with a switch/lever to make it 4x4. 99.9% of the time those trucks are in RWD mode, which means your cv shaft is not being used. It just free spins at most, transmitting no torque.

How long can it last like that? Basically forever.

Ah. I get what you're saying now.

That the wheel suspension and tie rods are the working components, absent power.

It definitely took more of an umph to get into 4WD late in life.