It all depends on the Admins, No matter how active your Forum Mods n other members are.
My forum
Candyman (Powered by Invision Power Board) used to be a very active forum with all the mods, VIP users, super mods n admins used to be online altogether everyday but then i went to a long tour n was absent from forum for a month and a half n when i returned, not even ghosts were there.
Soon after i returned, they started to get regular again n then came my broadband problem, i was off the internet for about 2 months due to internet problems in locality n again the same results.
I've seen this trend on many sites even those with oves 200k users.
Once there was a site SG (SymbianGalaxy.com) [now hacked n no longer exist], same was trends there. Same at xxxpda, mm, n many more.
As long as Admins are active (whether posting or not), their presence is enough n must.
take a cool example of this support forum itself.
Now Support is online everyday n mods also there.
But quite a time ago when he was away for an interval Mod activity was almost zero with some exceptions.
I Guess you get my point.