I'm just guessing here, but I wouldn't be surprised if they went the way Sony did with the PS2 did when the PS3 came out. Games will likely still be made for the DS and they'll probably keep them in production for a few years before they stop making new ones. You'd still be able to buy them from resellers after that, but they wouldn't be making new models.
Of course. DSi XL'S was just distributed to all the countries that it was going to be released for why would Nintendo abruptly stop production and sales? The same goes for Dsi's and the DS lite seeing as some games may require you to get certain things by sticking in a certain game in the GBA slot (ex. pokemon). I still see Gamecube's and PS2's for sale, heck even Game Boys. Why should this be any different? The only things that I can think of that get discontinued pretty quick are handheld games that are around 4 to 5 years old but that's only a certain percentage of them.