You would only lose your retirement if 100% of your savings was invested in company(s) that eventually went to zero.
Even if you're 100% equities, and concentrated in (e.g.) the S&P 500, that would mean that the five hundred largest companies in the US would have to go to zero before you would "lose" your retirement.
One could also go for a total US market fund (Russell 3000, $VTI) or total world market fund ($VT). Further, having a bit of bonds (10-20%) would allow you to be cushioned for things like the '00s, where the S&P 500 returned 0% for the decade:
* https://www.forbes.com/sites/advisor/2010/09/13/its-not-real...
If your retirement savings went down by 20% and you had to put off retirement by 5 years, but then you died after 5 years, you've lost your retirement!
Checkmate.
Of course, if a public pension fund is run this poorly, they will almost inevitably be bailed out at the cost of younger generations. Betting it all on one sector and refusing to blink when it looks like a bubble might be popping is not what I'd call competent management. That's just too much risk in the mix for a fund that needs to be there. If pension funds are overly exposed to one volatile sector, some really dumb people are about to lose their jobs, and rightfully so.