[verb た] + ら + [verb / i-adj / na-adj / noun] + ところだ
The grammar pattern たら~ところだ is used to express a hypothetical outcome that would have occurred if a certain condition had been met. It conveys the nuance of "if (something had happened), then (something undesirable/notable would have been the case)." It is used to reflect on a past situation with a sense of relief, regret, or alarm about what could have happened but didn't.
This pattern is closely related to the counterfactual conditional – similar to English "If I had done X, it would have been Y." The ところだ at the end emphasizes the critical point or situation that was narrowly avoided (or missed).
The most common usage is to express relief that something bad almost happened but was avoided.
It can also be used to talk about something desirable that would have happened if conditions had been different.