If your friend's mother has passed away and you are unable to attend in person, you can express your condolences and regrets to your friend. Here are some possible expressions:1"I'm so sorry to hear of your mother's passing. I can't come in person, but I want you to know that my heart is with you and I deeply deplore your loss. "
2."It is with great regret that I learn of the passing of your mother, a loss we cannot afford. I can't be here in person, but I want you to know that I will always miss her and grieve for her passing. "
3."I want you to know that I am very sorry to hear of your mother's passing. Although I cannot come in person, my heart is with you, and I will grieve for her passing. "
4."I am deeply saddened to hear the news of your mother's passing. I can't come in person, but I want you to know that I will always miss her and mourn her passing. "
Whichever expression you choose, try to keep in touch with your friend as much as possible, giving him comfort and support. At the same time, there are other ways to express your condolences and concern to your friends' family.