IRC isn't dead by any means. At the time of this post "There are 870,271 people in 531,400 chatrooms right now!" according to
www.searchirc.com (although I'm probably counted thrice). The channels and networks you used to frequent may have emptied, but IRC as a whole has not.
MSN, Google Talk, etc. may be more popular, but have a very different emphasis (1-to-1 conversation primarily with people you already know, as opposed to channels full of people you probably don't).
Finally, just in case you didn't realise, mIRC has been shareware for over a decade.
I'm willing to bet you'll be back
