If you take a step back and use some common sense its quite simple.
First off they would have to shut down the servers, which is a pain for EVERYONE involved. Then they would have to go in and manually apply a new weapon to Xur's inventory.
[b][u]And that is a much bigger deal than anyone on here seems to grasp[/u][/b]
Because obviously instead of it being the usual random weapon they will be having to choose a weapon. Obviously everyone and their mother will demand G-Horn, which we all know they would never do with it being in its current state.
Then once he comes back with Red Death or SUROS people would then just bitch and whine about it not being *Insert Exotic here*
As if that isn't bad enough then the "BUNGIE Y U DO DIS 2 US" threads would start and the "ITS ALL A CONSPIRACY TO KEEP G-HORN FROM US" threads would start. Leading to a FAR FAR bigger mess than Xur simply not having a weapon.
[b][u]TL;DR Bungie won't fix Xur this weekend because they know better than that. They know the community would then only whine and bitch about it not being the weapon they wanted it to be.[/u] [/b]
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They are whining and bitch anyways at least in that case they would bitch about something that isn't important and people would understand this. This just looks like they are too -blam!-ing lazy to do jackshit and don't want to take the time to fix an issue. What's looks worse. People bitching about them choosing a shitty gun or people bitching about a broken aspect of the game. PS... currently would take thunderlord over gally