Just had text from the wife of DH's best friend (and mum of DH's goddaughter) to say her dad died unexpectedly the other day. Climbed a ladder, lost consciousness and fell. She says they're all in shock but they're taking comfort from it happening quickly as he always said he wanted to go quickly.
DH and I met him 10 years ago at their wedding... neither of us really remember him 
Have started a message. DH says to write "Our condolences. Hope you all recover well from the shock" 
I think that sounds awful but can't come up with anything beyond "I'm so sorry to hear that" which also sounds daft.