Aftermath

Finding themselves locked in the caves, the party have the option of exploring the cave to defeat the monsters within, or they can try breaking out through the portcullis. The lizard folk view the party as a sacrifice, so they will actually guard the entrance and attempt to prevent the party from opening the gate, or escaping. They have six guards near the entrance, and will summon more if necessary.
If the party defeat the dragon, the guards seem to be aware and abandon the gate. When the party break out through the portcullis, they will find an abandoned village.
If the party are determined to locate the villagers, allow them to find evidence of their trail on a survival check (DC20). They clearly have an escape route, and are prepared to evacuate on short notice, so the evidence of their leaving is difficult to find. They have a concealed path that leads into a brackish stretch of mostly shallow water and small tufts of solid ground. They are adapted to the terrain, and willing to enter the water directly, which gives them advantage on any followers as far as escaping.
If the party are determined to find them, they can. Imogene will counsel against hunting them down, suggesting a better option is to escape the area and get clear of their reach while the sun lasts.
From here, I think we will start to see a shift in danger from scattered, sporadic encounters toward a more focused presence.