ooc: it was indeed the silver cords that tipped me off (opening a gate to the astral to let several asassins through physically would take alot of energy, and become a beacon for anything on the other side(ie mages like kadgar and magnus would have sensed it almost instantly, a chance that the lich would not likely have taken if the purpose of the assassins was to take us by surprise, not by brute force- the poison is a strong evidence of this, that they don't plan on beating us down, merely killing us with a glancing blow, or minor hit)
where as astral projection is a more subtle spell, and can be just as effective.
where Morguerat got this information(as well as knowledge of the Astral Dreadnought), well, that remains to be seen