Things go wrong. We're not stupid, we accept that. Lots of stuff is unavoidable when you implement changes to such a huge interlinked system. We'll be frustrated we can't play, but anyone with an ounce of sense knows you aren't doing it deliberately.
However, if we expect it as a distinct possibility, so should you. There should be an active presence on the forums whenever servers are down to pass on information and updates. Even when there isn't anything concrete to post, simply seeing a 'we're aware of the problem and looking into it' goes a long way to giving people confidence in your customer service.
With the size of the playerbase all straining at the bit to play, it has to be a justifiable financial expense to pay someone to sit on the forums during downtimes and immediately following them, just in case something like this happens. Someone to pat us on the head and tell us it'll be all right. Just a little bit of customer care, instead of silence and the feeling of being treated like mushrooms