Вопрос по – Сигналы в Qt автоматически отключаются при удалении одного из классов
QObject::~QObject Деструктор позаботится об этом:
All signals to and from the object are automatically disconnected, and any pending posted events for the object are removed from the event queue.
However, it is often safer to use
deleteLater() rather than deleting a QObject subclass directly.
Будьте осторожны, хотя:
Warning: Deleting a QObject while pending events are waiting to be delivered can cause a crash. You must not delete the QObject directly if it exists in a different thread than the one currently executing. Use deleteLater() instead, which will cause the event loop to delete the object after all pending events have been delivered to it.