But there is no way for mIRC to implement a $isonline() identifier because servers don't supply that information. The only exception being servers which support WATCH lists in which case you can have that information about a limited number of users (the exact number is usually provided as a token in raw 005 if WATCH is available - something like WATCH=128). If WATCH is available mIRC will automatically use that to implement the built-in notify list. If you have more users on your notify list than the maximum number of people that the server supports for WATCH then the rest are implemented with ISON which isn't really effective for what you want.
Basically, the only effective ways to do what you want is to require that users remain in at least one channel with the bot or require that they contact the bot via a DCC chat session.
