I'm supposed to be in zone 7 here in Victoria, BC.
Last winter I put my potted lemon verbena beside the house, north side. It got a little rain in that location, not much. I had cut it back to about 8 inches.
It came back this year. Beginner's luck?
My sister-in-law has her potted lemon verbena on her north-facing deck under a roof, it has come back at least once that I know of. She lives on the mainland and they have similar weather, maybe a little wetter over there.
I guess the slight protection of being beside the house, north-facing and under an overhang helped. And not being too wet in the pot.
Hope you try again, Deb!