Those who are in jobs that are physically demanding, who can't carry on doing them into their fifties or sixties, let alone their seventies, will just have to leave (or be made to leave) those jobs and find other work.
Or more likely, as they will find it very difficult to get other work, they will be claiming long-term unemployment or sickness benefits until they reach state pension age. And if they are over the Universal Credit limits, will get nothing, potentially for a decade or more, or until their savings and assets are depleted.
This is something we should expect and plan for. Could you cope with losing your job age 55 or 60 and funding a decade or so of living until you get the state pension, with nothing but a pittance of pre-retirement state benefits to live on?
If not, have a 'second career' in mind and make plans.