Even before the making of the last album, Johnson was concerned whether he was "still up to it" - maybe he had an inkling. Going deaf for a living, alright. He's done his service for AC/DC and rock'n'roll, not worth losing your hearing about it. BTW, Bon Scott was near-deaf at the end of his years with AC/DC too, their stage volume took no prisoners.
Status Quo have anounced that they will retire from "electric concerts" this year (unplugged and sitting down will continue), Francis Rossi, never one to mince words, says that "after each gig, these days everything f***ing hurts". And Rick Parfitt's most frequent organ is by now the bypass.
Back to the Aussies: Amazes me that they are even considering to continue without Brian J (forever in the shadown of Bon Scott, he nevertheless put his stamp on everything since Back in Black) - they might as well just put Angus on stage by himself if that is all that counts. AC/DC is not Rainbow, it's not like one man embodies the band.