I find it interesting that people spend so much time writing this stuff. IRC is what it is and it's not likely to change anytime soon, if ever. mIRC also isn't likely to become an IM look-alike client. IRC and IM are two entirely different entities and they will always be different.
If someone prefers IM, stick with it and don't bother with IRC. And vice versa. For those of us who like both, it isn't any problem to use both without expecting them to look alike.
If you want a client that acts more like an IM program than mIRC, there are some available.
Regardless, IRC isn't "losing ground to IM's" ... IM's have little to do with the number of people leaving IRC. IRC loses people more because so many people want the quick and easy and don't want anything more complicated than that. IM is simple. No networks, just nicks. Click, type. That's it. IRC is more complicated because it lets you do a LOT more. Many people prefer simple rather than having more features and abilities.
That is the main reason for a slow loss of people from IRC. Many just don't feel like being on IRC anymore. There aren't many new users because of the complexity. So the numbers are dropping. It's not because of IM.