I've now put in place some code which should minimise the amount of time the site is offline if this happens again - it runs every 5 minutes to fix the problem if it exists ... so if you do get a blank screen and forcing a page refresh doesn't help right away, leave it for 5 minutes and then try again.
The main reason the problem caused the site to be offline for so long was that both times it happened, I was on a plane all day and so wasn't around to fix it.