Dear Chaim,

If the Gemara ends with Tiyuvta, then this means total rejection. However, according to many, Kushya is not as severe. See at length in Yavin Shemu'ah 2:1 by Rav Shlomo Algazi that when the question comes from a Tana all agree that Kushya signifies that there is no rejection, just that the answer is not openly mentioned in the Gemara. If the question is from an Amora, there are two opinions if Kushya shows rejection.

Here the Beis Yosef writes that the unwritten answer is that we do not add Havdalah to Havineinu since one could err and think that therefore Havdalah requires a Berachah on its own (Levush) or that at least it would require repeating Shemoneh Esrei (Bach). So Havineinu should not be said.

Actually the Rashba and Ri ben Gias do hold l'Halachah to say Havineinu with Havdalah after Shabbos!

See also Posei'ach Sha'ar by Rav Noson Grossman on the Daf.

All the best,

Reuven Weiner