A new one has to be issued.
It happened to the flight I was supervising once; the pilots were not understanding why they were not receiving the FPL on the FMC... So the dispatcher had to print it and gave it to them.
Then the aircraft pushed back;
I had a look at the loadsheet and saw that it was not the correct registation; had to call to the tower to the aicraft come back to the apron. 45 mns lost, a huge cost to the company.... (fuel; pax that missed their tight connection at HUB)....