When it comes to GW’s the ONLY thing that really matters is do they pass traffic? Irrespective of what connection status says! And that’s where I agree with Nick that you need traffic to be sure (listen to the voice of experience! )
In V2 we have had a problem where GW’s would show as not connected - but a check in devices & apps would show traffic still routing through correctly = result!
Krishna correctly identified how systems and TTN back end ‘should’ behave but as Nick mentioned you need traffic to be 100% sure.
By way of example there was a recent multi-hour outage on V3 (TTS-CE) where they shed >1/3rd of previously connected GWs. Checking V3 console correctly showed my two recently (last month or so) added V3 test GW’s as disconnected. The system recovered and Console GW list showed them both connected again. A seperate issue I was seeing a day or so later where I wasnt getting expected data in a V3 TTNMapper integration led me to dig deeper - the two GW’s are in close proximity but slightly different locations and elevations which I know causes slight difference in coverage on other side of valley 1-3k away. When I dug into the V3 console I could see both GW’s showed connected and individually both GW’s looked to be online… I could see regular stream of traffic from trackers and a series of local static nodes on testgw041 but testgw040 was just sitting there showing ‘connected’ in the console (GW must have been happily sending its keep alive update messages & stats messages per Krishna’s comment) but live data window was empty and was telling me its was “waiting for…” i.e. no traffic was being seen/forwarded. I waited 24hrs to see if system recovered as part of the behavioural tests I was running. No joy so at that point I simply restarted the GW by power cycling it (suspect the GW PF stopped as a result of the connection being lost or a new connection being established _ didnt bother looking at the logs), instantly on recovery Console started to show the local node traffic comming through = result!. Without known local traffic, and fact it was missing, I would have happily have assumed GW was fine as V3 was showing all connected.
TL:DR = You need traffic to be 100% sure