If you only have one bot you will need to get a Mirc Chan Limit script for you or some of your Ops .... If the limit cant be raised then the bot cannot join. If you have more than one bot then the bots should be adjusting the chan limits so that they can rejoin.
If more than one Bot then look for a Limiter.tcl Like MC_8's mc.limit.tcl
It will allow the bots to change the chan limits in the channel and you can set how far ahead of the actual limit it will raise it.
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If you are running a botnet you might want to look into netbots which the bots will msg each other requesting a limit change if the limit exceeds them on their servers
"Knowledge is Power"
BeastNH/Moonster on Undernet/EFnet IRC Network