J.G.
I would still try to pump frequently (maybe every 4 hours or so for 10 minutes?) while you're away even if you're not getting much. It's very possible that your son will still be able to get milk from your breasts when you return.
I had a friend who went away for a 3 or 4 day trip and planned to wean her son while she was away. When she got back home he wanted to nurse and she thought that her milk supply was gone so she told him that she didn't have any more milk. When he kept insisting she put him to her breast so that he could "see" that the milk was gone but she was surprised to find that he was still able to nurse. So unfortunately (for her), she hasn't weaned him yet like she planned to. So maybe you will still be able to nurse once you get home.