Director Gardner gave up staying back to negotiate with Henrietta because he understood the Freedom Federation wasn't in a position to deal with the Black Rose Empire on equal terms.
The Freedom Federation's magitech industry may have boosted its influence to the peak of its time, but it was still nothing compared to the Black Rose Empire's potential.
He speculated that if nothing were done to change the status quo, the entire continent would be under the Black Rose Empire's control in under a year. That was how quickly the Black Rose Empire was developing.
Of course, the Black Rose Empire was already an untouchable existence if he factored in Vaan Raphna and the Red Dragon Clan.
It took Director Gardner three days to return to Freedom Federation with the help of a space-attribute witch from the Great House of Caelestis, which had recently started a fast travel service via its spatial magic.