The old will feel this in the prices they pay in the market for everything they need. A poorly functioning society will generate less in return for the value of the claims the old have built up.

And this all becomes a frightful problem if your society’s demographic shape permanently changes to being “top heavy”

Course that's not the only thing a pension is. It's also insurance against not knowing how long you'll live, being unable to feed yourself through to the end of life. We do that by pooling resources. The lucky ones die young, the unlucky get compensated by eating the claims of the lucky dead.

are you referring to "state pension" or all private pension holdings as well?