Sometimes plot twists are predictable when the problem has it's answer has been laid with the problem.

The amnesia thing that Taehyuk have is the consequence Hyo-un have by taking a risk by getting Taehyuk's name off the death list. Everything a person do to defy fate has a consequences. That's why after Teahyuk wakes up from being hospitalized after the accident the consequence for Hyo-un's action was Taehyuk having an amnesia.