[2020] What happens when the time runs out in the "Acrophobia" challenge? (MCC)

Hello,

I reinstalled the game yesterday and I noticed that in the challange hub, in the part that says "Halo 3 Celebration" it says that it will expire in 17H. What happens if it expires? Will it be impossible to get the new skull? Or will a new challenge appear to replace the current one (which it is to kill flying enemies)?

Appreciate any help.