I have read several threads regarding the gilsellers vanishing, and I can tell you that this will have little effect in the short term, and this is why:
People are starting to wonder if those leaping boots and sniper rings are going to become rare/ex, so they are all making a mad dash on the AH to sell them quickly. On some servers, there have been 40+ emperor hairpins for sale. This makes some people say "geez the only way I can sell mine is if I undercut, but if I do that I wont make much of a profit". This mentality is what is going to keep the prices up. You bought something for 400k, and you expect no less when you sell it. This is why prices will stay up. Even in this forum there was a thread about people complaining about undercutting and reducing profits. When I find the link I will re-edit the post and paste it.
In the long run, prices will eventually go down, but not by a whole lot. There is always going to be a large group of you who will want to get the same price, if not more, for the item for which you paid.
So if you think that by the gilsellers disappearing the price of strider boots will go from 5 million to 400k (or even 2 million), you're seriously mistaken. As long as someone is out there who believes that you should pay the same or more than he did, you'll be paying top gil.
edit:
here's the thread for people complaining about undercutting
http://ffxi.allakhazam.com/forum.html?forum=46&mid=109641955326543145&num=33
Edited, Thu Dec 2 12:34:16 2004 by Abzalom