Banshee lost his power, and indeed the ability to speak, in battle with Moses Magnum in Japan. While his power has returned, Banshee has never returned to the X-Men for more than a short while, until now, of course. He also has somewhat of a shady past, mostly around his days as a police officer and member of the British group Interpol. It has been revealed that he has some connection with Omega Red before he became known as that.
Most recently, Banshee's cousin, Black Tom Cassidy, showed his hideously scarred self at the institute with plans of taking the GenX kids under his rule, so he said. This was actually done for revenge against Banshee for taking away Theresa (Siryn), Banshee's daughter. For more information on that issue, see my review of Generation X #25.