Can remember off hand whether Spock is specifically stated to have left Starfleet, however he was "On Vulcan, apparently to stay" and had no intention of returning. Spock is certainly too methodical to have not properly resigned given that was his intention. look at how he put his affairs in order before going to Romulus.
Ummmm. my complete statement with regard to Spock.
Timo, I think you may have misquoted me.