Miller’s departure was confirmed by HBO to Variety:“The producers of Silicon Valley and T.J. Miller have mutually agreed that T.J. will not return for season 5. In Erlich Bachman, T.J. has brought to life an unforgettable character, and while his presence on the show will be missed, we appreciate his contribution and look forward to future collaborations.”

Source: HBO’s Silicon Valley gets renewed for fifth season, Erlich Bachman won’t return | TechCrunch