My dissertation advisor (committee chair) just informed me that he is severely ill and will leave the program very soon. His physical condition does not allow him to continue with any kind of advisory work, and that's happening all of a sudden.

We have been on this dissertation topic for almost 10 months, and I have drafted the proposal. The data has been collected and transcribed (not like we collected the data before the proposal but the data was already there and I transcribed them for partial sample analysis in the proposal). The original plan is to propose on April or May and do the defense by the end of summer.

Now I am still in the middle of shock and I don't know what to do next.

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Add: My department is a relatively small one, with a limited number of faculty members and each having really their own expertise. This makes the situation even more complicated as if I am going to switch to another advisor within the department-which I ultimately will have to-their expertise will not be a match to my advisor's and mine. This worries me a lot.