In good conditions you can go months without sending a single byte of traffic between an SSH server and client and both will pick up the connection just fine when it's time to communicate again.
You could cut off traffic between them for any amount of time and they would be none the wiser as long as the network connection is back to normal when they finally try to send traffic again.
(I had SSH sessions in a QA lab persist as if nothing had happened after the connection between the endpoints was down for almost a week while we replaced the aggregation layer routers. They never saw a link state change since the access layer switches were up the whole time. They never attempted to communicate while the connections between those were down, so there was never any problem as far as they were concerned.)
The keepalives and connection checks and so forth are mostly to account for things like stateful network gear (firewalls, NAT routers, etc) between the endpoints that will cease relaying traffic between them if they are quiet for too long.
In good conditions you can go months without sending a single byte of traffic between an SSH server and client and both will pick up the connection just fine when it's time to communicate again.
You could cut off traffic between them for any amount of time and they would be none the wiser as long as the network connection is back to normal when they finally try to send traffic again.
(I had SSH sessions in a QA lab persist as if nothing had happened after the connection between the endpoints was down for almost a week while we replaced the aggregation layer routers. They never saw a link state change since the access layer switches were up the whole time. They never attempted to communicate while the connections between those were down, so there was never any problem as far as they were concerned.)
The keepalives and connection checks and so forth are mostly to account for things like stateful network gear (firewalls, NAT routers, etc) between the endpoints that will cease relaying traffic between them if they are quiet for too long.