my theory:
the universe gave them three chances. the first time, things went wrong and jaeha died chasing yeonho. the second chance built a reality in the future that allowed future yeonho to communicated with past jaeha. the universe tried to fix the past using the future. however, that went wrong when yeonho died chasing after jaeha in the future. fixing the past using the future didn’t work, so the universe built a reality in the past instead where jaeha and yeonho are younger and together. the universe tried to fix the future using the past. things still went wrong, but yeonho was able to save jaeha because they were together, not chasing after one another.
or: yeonho survived after the second chance and they reunite after 10 years. jaeha didn’t answer because the link got cut when the universe saw the problem fixed.
no sad endings in this household!!
Back in Time to You