If one made Kiddush Shabbos morning on whiskey, and drank a melo lugmav of it, and then he eats a kezayis of pas to nullify the bitter taste, he is exempt from making hamotzi, since the pas is tofel. Is one yotzi seudos Shabbos in this way, even though he did not bless hamotzi and perhaps even did not wash (since the pas is tofel)? Does he need to bless after eating?
Technically if such a case would happen then you are right that he wouldn’t be yotza seudas shabbos since he won’t make a bracha achrona.
Practically however it isn’t applicable, since when someone makes Kiddush on shabbos morning, and he eats cake with the whiskey, he also means to eat the cake, as he is also hungry, and because if he doesn’t eat some cake he won’t be yotza kiddush in place of a meal, according to some poskim. Since he also intended to eat the cake he makes a bracha achrona.
Shmiras Shabbos Khilchoso chap. 54 ftnt, 63,:M:B 212-5, Shar Hatzion ibid 19, S:A O:C 253-4