Dear Mr. Li,
I have just learned with deep regret of the death of your wife and I am writing at once to express our heartfelt sympathy.
There is not much one can say at a time such as this, but those of us at the office who have met Mrs. Li would like you to know that you have our sincere sympathy in your bereavement. We recall her many kindnesses. She will be missed by all who knew her.
If there is any way in which we can be of any help, either now or later, do please let us know.
Yours sincerely
xxxx