The performer died after falling ill on stage. This was thought by the audience to be a part of the act, until emergency services were called in, the audience was evacuated, and he was declared dead at the scene by paramedics.
Until emergency services were called in, he lay dying on the floor.
What differentiates the subordinate usage in this example from the prepositional usage of until...just context alone?
Or is it because the the first example is written as a list of three clauses beginning with a subordinate 'until', as other than that, they appear the same.