mIRC isn't likely to become open source unless Khaled gets tired of working on it. And I don't think there's any reason to make it open source. If you want an open source IRC client, I'm sure there are some out there. They just aren't as popular. If you think something needs improved, you can add specific suggestion to the forums here and maybe they will be.
As for error handling, it depends on what exactly you are referring to. In most situations, error handling can be done very easily with the script that needs the error handling.
