We used bots to do that, but in todays world it's so easy to just stay logged in all the time, just leave a screen or tmux session running as a background process on a server
Would people pay for for a cloud service that bridged some of the gaps between Slack and IRC. Like notifications and offline message retention. Or would you just use Slack in those cases?
How would you do it without using screen, or bots as you say?
I am using Riot messenger. It can sync both Matrix and IRC accounts.