Ian,
The OGN servers have been 'down / offline' several times over the past year that I have been involved with OGN-R - with stations regularly showing on Onglide Range as 'Down' (Red), yet I know from personal experience that mine has often still been working as expected during these periods when it was reported as 'down'. I can't be sure of course that this is always the case though.
I think a big part of the problem is the fact that the OGN is an open source community project run by a group of volunteers, with most of the work - as is often the case - left to a few willing horses. I know from personal correspondence that the 'lead' software guys - including Sebastian Chaumontet, et al have been working very hard in the background to improve the system reliability.
Regards
Peter