Why think this? They would cut any finished content for dlc if they had to. After all that hullabaloo with Uncovered and the release of Kingsglaive, it would be critical and financial suicide.
I was only half-serious. Though, if they really realized "Nah, we can't release it like this, it would make more damage to the brand than the internet hate when we announce a delay", I could definitely see them do it, especially if it would just be 2 months more or so to glue everything together a bit more. As I said before in the grand scheme of things nobody remembers delays if the game is good in the end. See Uncharted 4, which was delayed thrice and nobody talks about that anymore. And FFXV will always be "the game that took 10 years", anyway - a few more months wouldn't make a difference. However you could just release it anyway, hope the strengths of the game are big enough to make most gamers overlook the technical flaws or bugs on release and iron it out over time with several patches, like The Witcher 3.