That's why mIRC beeps if the line is too long.
I don't think it checks the RAW to get the actual maximum length, but it's set to a value that should always be under the maximum length. So you should always get beeps before you reach the maximum line length for a network. Yes, a message would be easier to understand, but at the same time, the beeps warn you before you send so you can split your line before it gets chopped off rather than after.
