Getting the Marionette Lord to leave his body was far more taxing than Damien ever expected it to be.
No matter how much they claimed they would leave him alive, it was clear that they still felt unresigned about his survival.
Nevertheless, he eventually managed to convince them, not through any sort of negotiation or promise, but rather a certain strand of Divine Power that was residing in Damien's spiritual world.
Tiamat's will had gone into a hibernating state after their conversation, but her Divine Power was still present. Damien couldn't absorb it, nor did he want to carelessly release it into the atmosphere.
Therefore, while Tiamat herself wasn't present, traces of her existence were.
And as Damien learned through the Marionette Lord's quick exit after sensing those vestiges…
'Tiamat was an Emperor.'