What was the last name of the keyboard player that left the band?
The configuration of the band has evolved since first touring in 1988. Early incarnations of the band had three people playing guitars, drums, keyboards, and samplers.  Later incarnations replaced the keyboards and samplers with an additional guitarist, and incarnations after that added a multi-instrumentalist whose main role was as a bassist but also played guitars and keyboards on a number of songs. Finally, the live component of Nine Inch Nails has settled as a five-piece band since the Self Destruct tour from 1994. On the Performance 2007 tour, some songs from the Year Zero album were performed as a 3 piece band, featuring Reznor, keyboard player Alessandro Cortini and guitarist Aaron North, using a combination of live guitars and triggered loops. In September 2007, Reznor expressed his interest in moving away from the "rock band configuration" to explore "other ways [to] present the material in concert", though once again the 2008 incarnation consisted of five positions, but adding a variety of instruments not normally used in Nine Inch Nails such as double bass, various percussion instruments, steel guitar, vibraphone and other acoustic instruments as well as sampled sounds triggered from a variety of electronic instruments. No replacement was hired for keyboard player Alessandro Cortini after he left the band in late 2008, and the 2009 live band is a four-piece, with the role of keyboard player being shared between all members.
Describing the selection process, early contributor Chris Vrenna told Gannett News "coming from the same emotional background, I feel, is more important than how well you can play your instrument. That's one reason that makes our shows more intense when we're up there ... We found people that understood that. It makes us stronger".  Reznor described his selection of the earliest incarnations of the live band by saying "I'm not in the position to offer somebody a thousand dollars a week to rehearse ... So I took some young guys who were malleable, who would basically do what I want them to do but expand on it.  The only context I've worked with them in so far is, 'Here are the songs, here are your parts, learn them.' "Between major tours, live band members have on occasion contributed instrumental performances to official Nine Inch Nails releases, though creative control and direction has always been the responsibility of Reznor.  Live-band members who have contributed to major Nine Inch Nails studio releases are denoted by a "#" below.  Most members provide backing vocals during live performances.
Personnel
Live guestsMike Garson# – piano (September 2009 at the Henry Fonda Theater for the song "Just Like You Imagined")
Cortini