Employee dicovered to be an alcoholic.

Can anyone help?

An employee who has been with the Company since November 2009, he recently had two weeks off with what he told us was 'food poisoning' for which we paid him SSP. 

He has again been off since 16th August - unauthorised absence as we have been unable to contact him and he has not rung in.  After fearing for his life (the last conversation we had with him was when he told us he had had an EEG and had an enlarged heart) and contacting his next of kin we discovered that he has a history of alcoholism and of absenteeism and it now appears that he has not been ill on either ocassion but on an alcholic bender on both ocassions. Following this we went to his home and have spoken to him on the phone, he has said he is unable to work and unable to come in for a formal meeting. Based on this we have agreed to terminate his employment.

My questions are:

Does this constitute Gross Misconduct?

If this isn't Gross Misconduct, are we able to accept his resignation and treat his last two weeks absence as part of his notice period?

If not when should his notice period start from? 

We have paid him SSP to the end of the month as we thought he was genuinely ill, but should we deduct this from his final salary (if any) as he wasn't genuinely sick or adjust this against his final settlement as above?

I hope someone can help I am more than a little dumbfounded by this one.  Thank you