IMHO, demands are rarely the best approach. I would just bring it in and tell them it became unresponsive after the update then kindly express concern over being without your phone and let them know you appreciate anything they are able to do to fix or replace your phone. You may find the person more willing to work with you taking that approach.
Also keep in mind (assuming you rooted your Dx and loaded the leaked 2.2), that basing a replacement demand on the OTA failure after you modified your phone with an unofficial OS is probably not reasonable. I am totally for being innovative with gadgets with hacks/tweaks, etc., but anyone making the decision to do this should understand that they are risking bricking it or rendering it incapable of reverting to the official SW. Assuming you did root your phone, you may agree that its not reasonable placing the blame on the official OTA for messing it up. Verizon probably can offer you a workable solution even if it isn't a new phone.
Good Luck!