How hard would it be to take a well-linked site, completely change the subject matter & still retain link authority?

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So, this would be taking a domain with a domain authority of 50 (200 root domains, 3500 total links) and, for fictitious example, going from a subject matter like "Online Deals" to "The History Of Dentistry"... just totally unrelated new subject for the old/re-purposed domain.  The old content goes away entirely.

The domain name itself is a super vague .com name and has no exact match to anything either way. I'm wondering, if the DNS changed to different servers, it went from 1000 pages to a blog, ownership/contacts stayed the same, the missing pages were 301'd to the homepage, how would that fare in Google for the new homepage  focus and over what time frame? Assume the new terms are a reasonable match to the old domain authority and compete U.S.-wide... not local or international.

Bonus points for answers from folks who have actually done this.

Thanks... Darcy