No. It's not required. However I initially planned for midway rebuys but made a concession on rebuys just because it's not working here for there are so many posts that participants are gonna miss them for varied reasons.

You can participate without any rebuys. You can still win if your predictions go right and other participants go wrong. You just can't predict after the deadline, which is mentioned in every post, is over. So it's still a fair game for you and for everyone.