I'm slightly wary of the line
...penalising anybody because they have become ill or partially disabled...
because it clearly, repeatedly and understandably happens in civvy street. For example, it is common to have your driving license removed if you develop class 1 diabetes. If you were a driver for a living (HGV or taxi) then you would no longer be capable of doing the job. There would be no requirement to have you kicking around the dispatch office being paid the same wage you were on when driving unsocial hours.
Is it right to pay people for jobs they are not capable of doing? If so, we'll have to keep paying those poor hard-done-by premiership footballers all the way until their pensionable age even though they become physically incapable at achieving the job requirements in their 30s.