My Grandad was told late last year that he should undergo the same operation. He was told if he had it, there was a huge risk that he may not make it through the operation (can't remember the exact percentage they gave him) due to him previously having a heart attack. The other option was not to have it, enjoy the lifestyle he currently has but inevitably one day, his heart will go again.
I really cannot see how Kinnear can come back and continue to be the manager of a football club, nevermind a Premier League football club - it would kill him off.