This isn't a "crisis". Existing entitlement benefits are too high for the coming steady-state economy, but by like 30% or so. Adjustments will have to be made (e.g. some made-up numbers: we can work 10% longer careers, take 10% lower benefits, and expect a 10% boost in general productivity over this period), but we're hardly talking destitution or social upheaval here.
Retirees in the 2040's are going to see less resources-per-GDP dedicated to them than retirees in the 1980's for sure. But then they'll also have pervasive VR headsets and a plausible cure for cancer handy, so I'm guessing it'll be a wash.
Then we're long since doomed, because health care expenditure as a fraction of GDP (a rather larger pot of money than even retirement entitlements) has grown by like 700% (or whatever) over the last half century.
Time frames matter. The demographic change we're talking about is going to happen over the next 40 years, it's not like Black Tuesday.
Retirees in the 2040's are going to see less resources-per-GDP dedicated to them than retirees in the 1980's for sure. But then they'll also have pervasive VR headsets and a plausible cure for cancer handy, so I'm guessing it'll be a wash.