Recently my Google XMPP account in Telepathy/KDE went offline (according to my chat partner, who uses the Google+ web chat). The issue was that Telepathy/KDE did not notify me about this and the chat window still showed me and him as being online. Reproducible: Always
Are you sure the problem wasn't at the other side? Did you see other contacts in your list? Also I'm sorry but this bug report is not very useful, unless you can at least reliably reproduce the behavior.
I cannot guarantee that this was not a problem on the other end. However, after a while, I got the notification that the Google account got disconnected due to a network error. This might have been the 5 minute TCP timeout, even though it was more then 15 minutes according to the logs. The disconnect could also have been a bug (which I also observe with other account types), where the account gets disconnected seemingly randomly — and thus be unrelated to this problem. Would it be possible to decrease the timeout, or do some keep-alive ping-like stuff?
Any lower-than-ui stuff is unfortunately not handled by us, you'd need to file a bug against Telepathy at bugs.freedesktop.org and investigate there. Same goes with backend problems. You can provide debug logs as noted here: http://community.kde.org/KTp/FAQ#Providing_debug but if it's an actual backend problem, you'll have to take it upstream. Run the debug, connect and wait for your connection errors and post the output, thanks.
More than a year with no activity, closing this then.