It looks as if Doonican died of old age; the BBC who ran his weekly shows reports "His family said he died "peacefully" at a nursing home in Buckinghamshire. He had not been ill, but his daughter said his "batteries had just run out"."
We all have to 'go' sometime and that is as good a way as any and much better than many alternatives.
Val Doonican enjoyed a long career in the music business from 1963 until he retired in 2009. He is survived by his wife Lynn, daughters Sarah and Fiona and grandchildren Bethany and Scott.
More at the BBC