The moment they clear the gates of Sedom, the angelic pair splits. Genesis 19:17, in Targum Pseudo-Jonathan, makes the division of labor unmistakable.
"And it was that as they led them without, one of them returned into Sedom, to destroy it; and one remained with Lot, and said to him, Be merciful to your life; look not behind you, and stand not in all the plain; to the mountain escape, or you perish."
This is the Targum enforcing its own doctrine. Back in Genesis 18:16, it had already told us that each angel has exactly one mission. Three angels visited Abraham: one to announce Isaac, one to destroy Sodom, one to rescue Lot. Now that the destruction and rescue angels reach the plain, they separate and each does his single job.
The rescue-angel's warning is specific. "Be merciful to your life" (chus al nafshach) is an Aramaic idiom meaning "save your own soul, and do not look back." Do not stop in the plain — the whole plain is about to burn. Do not look back — turning around to witness judgment, the rabbis read, is a way of aligning yourself with what is being destroyed.
Lot's wife, in Genesis 19:26, will violate exactly this command and be turned to salt. The warning was not metaphorical.
The takeaway: when you are being rescued from a burning city, your job is to run, not to narrate.