I see the monitor kemba1-1a6a7hp has been dead for a few hours. I checked on a few pool servers. But it is still listed in the active list of servers, with a 20 score, which I guess was its last score. So, how long before a dead monitor is replaced?
Below is the graph of one server with kemba1-1a6a7hp high-lighted.
It will take some time before it drops, as it could have e.g. a power-failure.
But the ‘failing’ monitor has NO impact on your scoring as others still monitor you well.
The scoring of 1 (or more) monitor(s) have little impact as long as 1 or more score you as being good.
As long as you are above 10 your server is in the pool and active, but you still score 20.
So your server is found perfect regardless of the ‘failing’ monitor.
Don’t worry about that, they monitor system is very sophisticated and won’t drop you out of the pool because of such things happening.
Beware the testing-monitors also score you as double-check, but they don’t test as often as the active ones.
Many monitors need to fail before you see your overall-score drop below 20.
You can try this yourself by turn off your server for e.g. 1 hour, you see the score drop because ALL servers can’t contact you.
Hopefully this takes your worries away.
My question was because of curiosity and not worries.
The server I have shown isn’t mine and I wasn’t interested in increasing its score. I was just looking around at other ZA (South African) ntp pool servers and while looking noted that that particular monitor has been dead for a few hours. I checked on a few other pool servers and that monitor’s scoring stopped on them too. So that made me curious as to when a dead active monitor gets replaced, and being lazy I asked here rather than trying to search through the code. 
In the meantime that monitor came back up, although it looks like it is often dead / unavailable for a few hours.
I do not know how long it takes. Maybe @ask can tell you.
