I ran that encounter last night.
They had spent enough time chatting up the townsfolk to know about the tunnel, and came in through the cravasse. My players were within 2 intiative counts of throwing down with the Nothic when the cleric who (miraculously) rolled highest on initiative threw it some rations as a bribe. When it paused to devour them they threw it some more and he settled down. They made their way out of the crevasse and almost got into another fight with the Nothic when they started to try to loot his chest but backed off when he hissed at them.
They started to explore the cave however the sorcerer had cast a spell for some reason and wild surged himself into free teleports for 1 minute. He had been pestering the scouting monk all day with his message cantrip and now he teleported right behind him and whispered "I'm here." in his ear. Feeling jumpy the monk turned and attacked. The
gnome monk turned and attacked him. With a dagger. To the groin. One failed con save later an ear-piercingly girly scream attracted the attention of the Bugbears who tried to sneak in to investigate, but botched their stealth rolls leading to a stand up fight over the crevasse. After tossing three bugbear corpses to the Nothic (and narrowly avoiding accdently feeding him the gnome who got dropped by a single solid hit from a bugbear) the party seriously discussed retreating to rest, but felt they couldn't risk give the Redbrands time to prepare or respond. Then the monk went, alone for some reason, through the back of the secret door and took a drink from the cistern. Unfortunately the Redbrands from the storage room had heard the sounds of the fight and had hidden themselves in the room and attacking from surprise almost dropped the poor Monk, again. He ran screaming to get the rest of the party and another fight ensued. This time the party had little trouble as my dice decided to take the rest of the night off.
We had to call it a night there, but I don't think they'll retreat yet. I do think they are probably going to deal with the Redbrands without pause but rest and come back another day to deal with the Nothic who has them a bit freaked out. They seem to have sussed out that he is not an invested member of the bandit gang and won't really care what happens to the rest of the cellar complex.