There is one possibility. This may not be the right book, but certain elements do come close.
The Cosmic Rape (August 1958 Galaxy as "To Marry Medusa"; exp 1958; vt To Marry Medusa 1987) a Hive Mind from the stars invades mankind but finds itself – to its ultimate betterment – catalysing Homo sapiens as a racial entity into one Transcendent gestalt: the sense of homecoming generated by the final pages of this short book is deeply touching.
I only read the shorter version in Galaxy, perhaps there might have been more detail in the expanded novel version. What I do remember is that everybody could read everybody else's minds as they came together in the newly created human-alien hive mind.
Hope it helps. This has been a real challenge to find a book that comes close.