People write dissertations in Word all the time. How painful it is depends a bit on how complicated the dissertation is as a document. This is of course only

People write dissertations in Word all the time. How painful it is depends a bit on how complicated the dissertation is as a document. This is of course only an anecdote, but I know many people who started in word, gave up on it and moved to Tex/Latex, but nobody who went the other way (that is to say, I know people who tried to give up on Tex, but eventually went back - not anyone who actually published with it). This might have quite a bit to do with subject matter - Word has always been an awkward fit for mathematics.