Dear …
I was saddened to hear the news of __(name’s)__ death. Please accept my deepest condolences and sympathy to you and your staff over at __(name of firm)__.
I knew __(name)__ for __(#)__ years and considered it a pleasure to do business with __(him/her)__. I will never forget __(his/her)__ enormous capacity for helping people. __(name)__ was a fine (man/woman), one who will be greatly missed.
This is such a great loss to your company and to our community as a whole. My thoughts and prayers are with you during this time of sorrow.
Sincerely,