One for all and all for one 6

We can initially assume that 25% of the total number of participants will withdraw. If 80 people registered, then realistically, we'll have at best 60.
We should immediately create a tournament scheme based on the assumption that we have around 80 participants, but in reality, only 60 will play. And individual withdrawals will, of course, be a reason to keep a separate list of them (I personally enjoy doing that), but it won't affect the tournament.
(25% is an optimistic figure; the real percentage of problematic players is 30-40% in one way or another).