It sounds to me (as a sober alcoholic for six years) like he is handling it very well, exactly the way he should. I know many, many people in AA that have gotten through horrible tragedies (loss of a young child, etc.) with the support of their fellow AA members. Those people will be the ones to support his sobriety. You can support HIM by simply being there to listen.
As for your work trip, I would tell your husband that you would be glad to cancel if he needs or wants you around for a few days. If he tells you to go, I'd go. You cannot "manage" his sobriety by staying home, and at fifteen months, he knows what to do. In terms of maintaining his sobriety, his AA friends will be far more helpful than you.
Learning to deal with loss, sadness, anger, and other strong emotions without picking up a drink is one of the most important things we do in recovery. Life is full of things that bring on those emotions, and each time *I* got through something difficult, the easier it was the next time.
I'm sorry for your loss. He can make it through this and so can you.