“But is he just a big pothead or is/was he big into the hard stuff”
Heroin addict.
I have no idea if he still is.
Good Lord.
I can see the human body surviving for quite a while even if you beat and batter it...but I would NOT expect the person to be able to function almost at all..no less tour with a band.
Most of the Stones are old and alive.
Maybe they made a deal with the devil :)
I’m joking but maybe something like that is possible.
That is not my area of expertise :)