Players (level 2) got themselves in a very dangerous encounter, do you have any advice ?

Hi, I’m DMing a homebrew adventure for the first time and my PCs got themselves into a very dangerous situation.

They were supposed to discover a kobold tribe while exploring a cave and have multiple fights in separate rooms as they went deeper. BUT—

They decided to avoid combat entirely and managed, with some really impressive rolls, to convince a few kobolds that they were working for a dragon and were there to see the Queen of the tribe. Maybe I shouldn’t have allowed it, but I thought it was fun and well-played on their part.

So they made it all the way to the heart of the lair and then tried to steal the Queen’s treasure. But since they haven’t defeated anyone, all the kobolds from the previous rooms are able to come and fight them, making the encounter extremely hard and potentially lethal. PCs are only level 2, it would be disapointing to have a TPK this early. We ended the session after rolling initiative. I have some time to prep. What are your advices ?