Diablo 3's first expansion, Reaper of Souls, launches at midnight tonight - in fact, if you're in the UK, a bit earlier at 11pm GMT - and the mood among players is upbeat. A month ago, Blizzard released the 2.0.1 patch which introduced many of the base changes of the expansion; it's been well received, while last week the decidedly less popular auction house for trading items was turned off.But some are still wary that, come tomorrow, they may not be able to play the game at all. Diablo 3 is an always online game and its launch in May 2012 was marked by stellar sales and disastrous service, as the famous Error 37 denied many players access. Is there a chance that the influx of players brought by the expansion will cause history to repeat?"I think it'll be fine," lead producer Alex Mayberry told me in a London hotel today, sounding confident. The reason for his confidence? That patch, which means that players have effectively been playing the expansion, and Blizzard testing its performance, for four weeks now."When 2.0.1 went live a couple of weeks ago, that was the same codebase as Reaper. I mean, it is Reaper with Act 5, Crusader and Adventure Mode turned off," Mayberry explained. "Come tonight when it's time to launch, we just turn those things on." It will even be possible for players to log in before their local launch time tonight and play the game as normal; the expansion features will become available in-game at the allotted time without them having to log out or patch."We planned it out this way," said Mayberry. "We planned to give ourselves a good month of time where we could get the code out, get people on and resolve issues. The worst part is going live and having all these issues and having to resolve them while players are upset. It's much easier to do this pre-patch and then have the time to react to the things we saw, especially on the server side."Everything's looking really good for tonight... Volume of people plus new code usually equals problems, so we've got the code out, we believe the infrastructure's in place - I don't anticipate that degree of problems that we had at the initial launch. I think it's going to be fun."