The following all happens in a town and the nearby surrounding area.

So my party, hereby referred to as their classes are currently third level and have infiltrated a cults hideout, they went there looking for Rogues friend and snuck in with disguises and managed to bluff their way into where the friend was being held. She was in a holding cell. After some deliberation they devised a plan to cast silent image and sneak her out, they couldn't manage to pick the lock and Cleric smashed the door in, this was heard by nearby cultists and they decided to just make a break for it. The cult massively outnumbered them and the party got surrounded. Sorcerer, who is an Aasimar and can fly at 3rd level, flew past everyone and escaped while the rest of the party surrendered. We ended the session there and Sorcerer told me after the session that they plan to go to Cleric's tavern to get the barkeep and any tough looking patrons to form a quick mob.

The conundrum here is that I can't think of a good reason for these cultists to not just kill the party aside from that's not fun. The cult is aware that one of them escaped is probably going to bring the law down on them, so they'll also want to leave. If I was them (and in a way I am) I'd probably kill the witnesses and bail.

Any advice?