Hello, Idontknow.
There is, until now, no official responde to that, but according to Tibia Rules,
"Violating or attempting to violate the Tibia Rules may lead to a temporary suspension of characters and accounts. In severe cases the removal or modification of character skills, attributes and belongings, as well as the permanent removal of characters and accounts without any compensation may be considered."
So, depending of which misconducts someone does, CipSoft can reserve the right to bannish the person, including taking the Pantibian privileges. Becoming a red skull, though, won't probably be one, since it is legal to become one.
Today (28/01/2022), Cip made a new announcement concerning on staying qualified, as we can see below:
In order to qualify, players have to be ranked among the top 50 in the Pantheon Highscore of their respective region. To stay qualified, players in the top 50 have to observe the following:
If a character in the top 50 is traded after the festivities, neither buyer nor seller can join the Pantibian Festival, resulting in one less invitation to the event. Disqualified characters are marked with a red X in the highscore.
So, yes, now it is guaranteed that there are certain conditions in which you'll be excluded from the festival even if you get the top 50