You do not need to file Form 8832 and the filing is not somehow retroactive (you are filing a final 1065 for a particular tax year, most likely calendar year 2018).
You might want to read the recommended post in the thread at the link below as it contains comprehensive information on this issue (although it involves a buyout scenario).
https://ttlc.intuit.com/community/business-taxes/discussion/re-purchased-partner-s-50-ownership-of-a...
