It's an interesting thought, but seeing as how the DSi will have full compatibility with DS games, and DS wi-fi, I don't think the servers will be going anywhere for a while. If anything, the DSi seems more geared towards wi-fi interactivity than the DS. I would imagine they are more focused on actually upgrading their wi-fi infrastructure to handle the new business model that download-able paid content provides.
In short, I think that the servers will remain long after most people's interest in DS wi-fi has faded and been long forgotten.