If there is no underlying problem, and he passes all UCI health checks, then I think it'll be his decision if he returns or not. Hopefully he'll take his time and consult with a range of experts on possible issues before any decision is made.
Added later: Apparently the cause was an 'unstable cardiac arrhythmia'. I can think of quite a few pro cyclists who've suffered from tachycardia, Stuart O'Grady for one, so it doesn't seem to be necessarily career ending.
An arrhythmia getting to the point of haemodynanic instability requiring defibrillation is unlikely to be just a simple tachycardia - more likely a serious arrhythmia, potentially with underlying structural cause a la all the collapsing footballers, which require a more cautious approach.
What insurance are you thinking of?
If there is no underlying problem, and he passes all UCI health checks, then I think it'll be his decision if he returns or not. Hopefully he'll take his time and consult with a range of experts on possible issues before any decision is made.
Added later: Apparently the cause was an 'unstable cardiac arrhythmia'. I can think of quite a few pro cyclists who've suffered from tachycardia, Stuart O'Grady for one, so it doesn't seem to be necessarily career ending.