Well, he didn't really leave, as much as he was replaced. After one whole month, the team has already decided to change things up - again - bringing in xfl0ud, a young Turkish talent.
Apparently, the Lithuanian was struggling to fit in to the team's system, and things just didn't work out. To be honest here, this is probably the smartest thing to do. A lot of teams keep members on - especially ones with a stature like EspiranTo - and try to work out differences and issues, but with the team being so young and still not much more than a mix, you have to make a decision.
An organisation could support players with this, but of course, GORILLAZ' new organisation is yet to be unveiled. Who could it be?