A disconnected sender does not produce an error you see. It produces a slightly lower send count, which looks like a quiet week until somebody adds it up.
Why this needs its own check
Sending tools report on what they sent. They do not prominently report on what they did not send because a sender went offline. From the reporting side a disconnected inbox looks identical to an inbox with nothing scheduled.
Over a week that is a meaningful volume shortfall attributed to nothing. Over a month it is a campaign that looks like it underperformed when actually it barely ran.
Switched off and left off
The most common cause is not a technical failure. Somebody disables a seat for a reason, the reason passes, and nobody re-enables it. That is caught here too, because the effect is identical.
It reports
Reconnection is a credential operation and stays a human one. This finds the problem and names it; a person fixes it.
Runs well with
Skills compound. These are the ones we usually install alongside it.