Can a player collect nobles after a day ends in Guillotine?
The day doesn't end when the line becomes empty.  It ends at the beginning of someone's turn if the line is empty.

After your friend plays Escape!, the line is randomized and two nobles discarded, resulting in an empty line.  Your friend tries and fails to collect the first noble in line (there no longer is one).  Then the day ends, a new day begins, and twelve new nobles are added to the line.

Your friend is out of luck, I'm afraid!  No noble for him until at least his next turn.