Impact of gap year during phd program on future post-doc and employment options?
It is not uncommon to have a break doing a PhD program, especially in the U.S. where it normally takes longer than in other countries. A list of reasons to have a gap includes maternity, health conditions, family situations (in some countries / cultures), or even temporary financial reasons. All these explanations seem fair to me, and I would not hold such them against the candidate.

What is very important, though, is


how (and whether) you will address the gap in your cover letter 
how your supervisor will speak about this in the recommendation letter.


If you are open to your colleagues and do not let them down without a reason (in other words, if you are doing your best given the situation), I do not see why the situation itself should be held against you and diminish your chances of future success.