I myself an a Millenial and I believe that the world is unlikely to look the same when I am old as it does now, though I don't think there will be a full-blown apocalypse and I don't think that money will suddenly not exist or anything. I'm a big fan of John Michael Greer's theory of catabolic collapse, i.e., a slower collapse that proceeds in stages.
HOWEVER.
I am still saving for (early) retirement, because: a) if everything does proceed as normal it will be helpful and frankly my own savings seem more likely to exist than government pensions; b) if I can ER in a low enough number of years then society probably won't have changed as much by that point, so I can still use my ER (or even part time semi-ER starting earlier) to enjoy the fruits of our civilisation before they go away; c) in the case that civilisation DOES start collapsing in such a way that money becomes useless, a frugal lifestyle, especially ERE-style, will have given me a much more useful skillset than consumerism and office life, so I'll still be in a better position than I would have been otherwise.
For point c), for instance, after I read Seneca (and MMM) on voluntary discomfort I started sleeping on a mat on the floor rather than a bed, which means I care much less about having access to a bed. My income isn't particularly high because I'm within the first year of self employment, which means that to get FIRE savings percentages I have to be creatively frugal rather than just spending less, which means I can use some of the same creative ideas in the collapse situation. Generally, in fact, being frugal at a level of less than £10,000 spending per adult earner per year, or even less still, is excellent for applying JMG's old tagline, "Collapse now and avoid the rush." So really, FIRE makes sense whether society collapses or not.