Hey guys, my party is playing through Curse of Strahd and has just reach Vallaki. One of the party members tried tracking Rudolph while he was going to his cart, but lost track of him. Meanwhile, a couple other party members went to the church and learned about the missing bones. They rallied the rest of the party and went to go track down the bones. When they reached the coffin maker's shop, the threatened him into telling them were the bones were, and the paladin retrieved them. As they were leaving, they were attacked by three vampire spawn, but it was getting late IRL when combat started. Given that my party is level 4 and each spawn is CR 5, I figured it was going to take much longer to finish the fight than people had energy for, so I had Rudolph join them halfway through the fight. By the time they were down to the last spawn, the cleric had been down, the rest of the party wasn't looking too great both on and off the table, and the vampire still had 70 hp, so I had Rudolph cast dispel evil and good and modified it to allow him to banish the spawn back to Ravenloft. Afterwards, he told the players that he had been staking out the town trying to find a good time to wipe out the vampire nest, but his plans had been ruined. He then packed his stuff, left Vallaki, and headed back to his tower. We called it after that because of how late it was, but I wasn't happy with how it ended because I don't like using NPCs to end a fight, my players are convinced that I was just pulling punches to avoid a TPK, and it was an anti-climatic end to a rather good RP session to get the bones. How do I bounce back from this in the next session?