Unresponsive advisor, job offer in limbo I'm in a rough place right now in the homestretch of my PhD, and I'm looking for advice. I've recently reached out to my advisor about this, but they are not responding to my emails, hence me asking this question here. 

My advisor is on sabbatical this year (my final year of my graduate program). Three months ago, I sent my advisor a more-or-less complete draft of my thesis, and I have not heard anything at all from them since. No edits, no comments, nothing. In part, I feel responsible for this situation; I was slated to finish last year, before my advisor left, and now they are having to edit my thesis while on sabbatical. I realize that this is a big burden. I am not sure whether or not I have the right to be upset about how long this has taken as a result. 

My main concern that I have is that I want to defend before September 1st, as I have an academic job that is set to begin on that date (contingent on me actually being awarded a PhD). In order to give committee members enough time to review my thesis and for my university to process the necessary paperwork, I will likely need to have edits incorporated into my thesis by the first week or two of July. Given how long this is taking, I am not sure if this is possible anymore, and I am not sure who is ultimately to blame here.

My main question is this: Is it out of the question for someone in my position to ask their new employer whether or not it is OK to defend their PhD after the start date of their new job? Would I most likely have the offer revoked if I do so? I realize that there is know surefire way of knowing without actually asking, but I'm looking for some advice before potentially shooting myself in the foot here.
I'm going to just guess that meeting your tight deadlines will be impossible with an advisor on sabbatical. So you need some short term action that will preserve your position. 

You can certainly ask a new employer about starting before you have officially received the degree and they might be fine with that, or not. But it would be more likely to be a positive decision if they had some quasi official assurance that your timely and successful completion is not in doubt. 

You might try one or both of the following. Ask your advisor for a letter, assuring the reader (your potential employer) that completion is a pretty much pro forma situation. "We need to dot some i's and cross some t's etc." 

Go to the department head and get confirmation of the above and even his/her help in getting that letter from your advisor. The head might also include an additional supporting letter, confirming that your progress is on track, etc. 

Many employers would be supportive as long as the situation doesn't seem like it will go on and you wind up ABD or unable to do the job you are being hired for. Of course, there may be some situations in which there are firm, legal, requirements that you get the degree before starting the job, but those are likely rare. But I'm assuming this is an industrial job, not an academic position, which might well have firm requirements to start. 

Another option, perhaps, is to ask the employer for a delayed start date. But that request would also be positively supported by the sort of letter(s) mentioned above.