Advisor on medical leave only a few weeks before dissertation defense My doctoral advisor has been on medical leave for several months now. As such, he has been extremely hard to maintain contact with. He lives in a different part of the country and checks email only about one or two times a week. This usually has not been a huge issue because I know what I need to do for my dissertation and have been doing it. 

In keeping with a discussion that he and I had about three months ago (which was a continuation of several prior discussions on the same topic), I have agreed to terms for a full-time job starting in six weeks. Part of the contingencies of the job require that I actually have successfully defended my dissertation. 

Today, he sent me a terse email to inform me that he needs to take care of some of his medical issues, and then he will contact me and we can try to "finish" the dissertation. This is a deviation from previous agreements he and I had. Outside of any last edits he would want to add though, the chapters for the dissertation have been done for some time now. I am just biding my time, waiting for him to give the final go ahead to submit the dissertation to the committee. I have conveyed these thoughts in email to him, but he has ignored these emails. 

My question is this: Has anyone ever declared their advisor "medically unavailable" just weeks before trying to defend their dissertation? I am essentially faced with the decision of delaying the start date for my job (while still paying rent all the while) and keeping in the good graces of my absent advisor, or, alternatively, going to my department and seeking to have my advisor declared medically unavailable. Because he would possibly still need to sign off on my defense paperwork, I am worried that my advisor could try something to still block me by refusing to consent to signing the paperwork. 

ADDED

I will add here a few details about why my advisor is on medical leave. He is not sick or dying. He had a routine procedure done on his knee about five or so months ago. Millions of people have undergone this procedure and return to work within a week. This is not a case of a poor old man who is terminally ill. I do not think it is unreasonable to ask a guy who had routine knee surgery to respond to emails five months after the surgery.
Something (somewhat) similar happened to a friend of mine. The key to her solution was to get another chair while at the same time allowing her advisor to "save face" in the department. Basically she made it a matter of logistics (rather than irresponsibility or personality). 

She approached another (full professor) member of her committee to act as an ally. Then she copied the ally on a friendly email to her chair suggesting that the ally had "volunteered" to be a "co-chair" for the logistical purposes of the defense/graduate school paperwork. She explained that of course she wanted to keep her original advisor as the chair, but that the work start date seemed like it was making that arrangement impossible. She and her ally were able to arrange it so the original, medically unavailable chair would still get credit internally for having her as a student and would remain on the committee (as a "distance"/Skype examiner). 

I have found that, in general, difficult professors respond to subtle pressure from their peers (never their students) and prefer solutions where they can save face!