From: Rabbi Moshe Sofer
To: Rabbi Shmuel of Brody
After a marriage was consummated in form (nissu'in) but not physically, and the husband was then divorced due to a discovered blemish, the question arose whether the wife must return the kiddushin ring. The Chasam Sofer concludes that since this was a divorce from nissu'in rather than eirusin, the gezeirah against returning kiddushin does not apply, and combining the Maharil's ruling, the Rema's endorsement, and an umdena-based analysis, it is close to certain that the wife must return the ring; at minimum a compromise is warranted.
Source: Shu"t Chasam Sofer EH I §105