Unless your attendance will prevent someone else from going that has known him a long time, you should go.
Between now and then, make sure you know your company's policies and benefits as they relate to this situation. Insurance contacts, grief counseling, paid versus unpaid time off, etc., so that when he has questions you can help. In the midst of his grief and stress, he'll be dealing with family (any kids?), dispositioning the will, getting her credit cards stopped, hassling with insurance companies, having her IDs cancelled, and a thousand other things I can't recall right now. ANYthing you can do to relieve some burden, or at least help him find answers, will be appreciated.
When I've had an employee lose a family member, besides expressing my sympathy and offering condolences, I tell them something like "Don't worry about this place. I want you here when you can be here, but more importantly I want you to take whatever time you need to be away. You'll be busy with all sorts of arrangements and I don't want you to worry about work on top of it. Do the best you can to let me know when you'll be out so I can arrange coverage, but if you need to leave just leave and we'll sort it out. Let me know whatever I or the company can do to help."
If it's someone I know well, the conversation will of course be more personal, but in any case I want to do my best to take away any work stress.
Be aware that there's usually an emotional cratar a while afterward, maybe a few weeks. Initially he'll be busy and there will be family and friends all around, but when things transition to the new "normal" is when reality sets in and serious sadness and depression take hold. Keep and eye on him and help as you can.