This happened on the CSI shows all the time, though there were times when they gave the characters a send-off, but some disappeared without a trace. There was a female lab technician on CSI: Vegas who was written out of the show after several seasons. She said she was going to back to Oregon or Washington to live with her sister and work in a lab there. The producers said they were "going in a different direction," but I didn't see any different direction. The same thing happened with Eddie Cibirian on CSI: Miami. The producers had him killed off, because they wanted to focus on the "core" cast members - Horatio, Delko, Calleigh, Natalia, Walter, and Ryan. They didn't have room for one more?

As for Lenkov, he was indifferent to the original show from the beginning, with the bad casting and bad writing.