I tried to feign death, that failed as I was dragged before Alarak and he stated if I had anything of title use to tell him, I said no, so he deemed me useless and punted my Paladin, sending him flying across the room and slamming back first into a pillar as the DM stated I heard crunching sounds and then had to roll a Death Saving throw, I succeeded (thankfully) and then was reduced to 1 HP. I laid on the ground, waited for Alarak to leave, then stated I weakly raise my arm to flip him off as he walks out and then place my hand to my chest and pumped 20 points from my divine pool into myself to heal. I then played Paladin turned Rogue and started sneaking around, managed to ambush a guard, killed him, put on his armour and then started walking among them. Rolling at advantage for deception to move passed them. Reunited with my party and we managed to escape.
With Medieval tech it would be hard to fight a war in a cavern system. The title problem would be light. If you used a torch you would be seen before you got to the enemy. If you didn’t you couldn’t see. Defenses would fortify chambers and if the chambers were large enough (Menzoberranzan) you may consider having castles in the chamber. Attacks would be done by having scouts crawl along tunnels in the dark and emplace ropes that the other attackers would follow. At the last minute they would fling flaming moss or arrows onto the enemy ramparts to light the way which would be the signal to attack. RA Salvatore did an excellent job describing medieval warfare with magic in the Dark Elf trilogy except the dark caverns are lit up by a pillar if I remember right.