Yeah these events deal with that single connection to the server. Not the channels. $server or $network should return where the connection is connected to. There are many tools to access data from a single connection like scid, or scon.
If you want to know what channels you had open on a single connection that disconnected, $chan(0) returns total channels like normal. And therefore, $chan(1), $chan(2), etc. will return the individual channel names. I prefer these over $comchan.
$chan has no place in disconnect or quit so of course $chan would be $null.
Documentation of "hidden" features can be found in the version.txt file thought its a very long and boring read.