Well given the hypothetical circumstances, if mIRC didn't exist, then yes its highly possible that other clients would be used. Now whether or not people like/dislike these clients is their personal choice, however since this is a hypothetical question that mIRC doesn't exist, you really don't have much of a choice. Either use a client you do not like, or just simply not chat. But mIRC does indeed exist and will probably continue to dominate all other chat clients that are available.