Issues with unfinished PhD
As @Alexandros said, it is not clear why you would be risking your health, should you decide to finish the program. Working remotely on dissertation is certainly feasible (I've done that personally), if your committee doesn't mind and the program allows it. However, defending dissertation remotely might be more challenging to obtain permission to, but still possible. All that very much depends on your university, the program office and, to a lesser degree, the faculty involved. In regard to your specific questions, they are IMHO very broad and, thus, impossible to answer without knowing lots of personal circumstances and even after that the advice could be taken with a huge grain of salt.