ちなReactiveSwiftの on オペレーターではterminatedとdisposedは分離されてます https://github.com/ReactiveCocoa/ReactiveSwift/blob/bb2a2d6f422f79ebc86a755642ca9bd106578d12/Sources/Signal.swift#L886-L924 (edited)

ReactiveCocoa/ReactiveSwift

ReactiveSwift - Streams of values over time

3