Weird main pulley failure. HELP....

[WVOtoGO]

1980 300D. No turbo. 280K+

I’m driving down the road today. All’s well. Then all of the sudden, I loose power steering. Then about a quarter of a mile down the road I notice the temp gauge screaming for the red-line, and the battery light comes on. Engine at idle, I coast into a parking lot and shut it down. Water boiling out of the overflow. Open the hood, thinking I’m going to see some missing belts, but no. All the belts are fine, but the main pulley is no longer connected to the crankshaft. The harmonic balancer is fine, and still attached to the crank but the main pulley assembly will slide right out the front of it. I can see the bolt holes in the back of the pulley assembly. They look fine. I can’t get the assembly out, do to the A/C hose in the way, and will have to tow the car home to pull the fan, etc to get it out through the top. I haven’t reached into the harmonic balancer to see if the (6 ??) bolts have sheared off, or just backed out.

Has anyone else experienced this? Is there a trick to pulling the balancer off if I need to? Special puller?
What are the odds of those (6 ??) bolts coming out? I’ve never touched them in 26 years. I don’t mind a failure with a 26 year old car now and then, but this one seems rather odd.