My experience is only GM A bodies, but they use a steel retainer, not a rubber grommet or boot. My limited surfing of the 'net suggests that is what some other cars use. I wouldn't trust a rubber grommet. I'd back it up with a strap bolted across the pushrod area, with a hole or slot for the pushrod. when I assembled my current 66 with a GM type dual master cylinder, it didn't look like the rod could fall out of the deep recess in the master cylinder, but I was anal and scoured junkyards until I found the correct retainer. The yard had a dual master cylinder hanging on the wall, with pushrod and retainer still attached, and wouldn't sell just the parts I wanted. So, I paid the whole $5 or 10 and then threw away the cylinder.
I am so sorry to read about your tragedy and hope no one assumes the stock or aftermarket master cylinder setup is "good enough" in the future. I didn't even give my worry any vocalization, assuming others knew what to do, or that I was excessively detail-oriented. There are so many things that can go wrong, and it is through forums like this that we seek them out and fix them. For example, I run a full face helmet SA2005 and "assumed" it was good protection for the lower jaw. Your experience shows that the steering column can still be an issue.