What will happen if my phase 2 for SLC has to be cancelled since my phase 1 is still on "wait" status?

There are phases for SLC?

They can reschedule you for a later date after your phase one has been completed.

If your phase 1 rolls into a reservation, you'll attend phase 1 and then you'll have to find a phase 2 class to apply for. If your class' phase 2 does go ahead, you can ask to stay as a walk-on.
Depending on the number of instructors and the size of the classroom they usually accept you.