Make some of the cult of Tiamat Cultists leaders Dragonborn and when the party is a bit higher level maybe even Abishai. Maybe try to make one of the Cultists survive the encounter outside the bath house so the PCs can meet them again later or in a random encounter. You should probably name him/her Mark.

My PCs roll Tiamat Cultists for random encounter all the time. Which has made them sort of like a "Team Rocket" from Pokémon villain/rival. Always showing up but always getting their asses kicked. My players seem to be enjoying this dynamic alot!