Except they didn't 'finish PES off', the series is still going, as a cheap unfinished card game that subsists off whales.
Again, they may not be able to delay further than March, or potentially a couple of months after that. The fear is that if they have nothing to show in January, then even May/June is too soo. If they are forced to put something out, like many a sports game preceding them (eg Ashes Cricket 2013, and the like), it may end up being an 'early access' game as a service Football Manager.
It can be more complicated than that. Penalty clauses, etc, aren't out of the question for this kind of thing. If the losses would be large enough, it may just make sense to cop a the reputation hit and release something unfinished. We've seen it all before (eFootball, Ashes Cricket 2013, various Rugby games), or as noted above, it could trigger a move to a game as a service model.
The fact is that in all the discussion that has followed their silence, they have remained silent. That only happens when there are real problems behind the scenes. They can't point to: 'it's not time yet', as they are past their own deadline. The likely reason they are staying silent because the speculation is ultimately less damaging than the actual situation.