Though the FDA generally tries to adhere to PDUFA dates, they aren't set in stone, and it's not unheard of for the FDA to extend a PDUFA date. This generally happens when the FDA needs more time to complete the review process.
The ramifications of moving the PDUFA date for Vascepa will gut CDER DMEP. I will move to eliminate the DMEP and have already started the process today./-BB