The zombie dodges the initial jet of flame, then seems to forget about it, as both undead in the room focus on Sabian. It gets burned, but is not dead.
Spoiler
ZA
Attack (1d20+3)[21] for (1d6+1)[2]
ZD
Attack (1d20+3)[9] for (1d6+1)[6]
ZA Bonfire (1d8)[4] Dex DC 14
(1d20-2)[7]
Expected Undead Fort save (1d20+3)[16]
=> Party
If everyone is just exiting the first floor as fast as possible (no more fighting/attacking), please discuss/specify where you're going.