I found this interesting. There is more online for you to research: apparently in early stages reasoning is not always involved, but as the disease progresses it does seem to involve reasoning and other abilities. As you can imagine, without language this is all difficult to assess. Some measurements said average lifespan after diagnosis is 12 years. This seems long to me, but I honestly don't know:
https://www.brain.northwestern.edu/pdfs/PPA/PPAInformation2016.pdf
https://www.aphasia.org/aphasia-resources/primary-progressive-aphasia/