It's probably Nick. He doesn't have time to film, he already has Kingdom Season 2, his new movie "Goat", his tour Same with Ariana. They'll be the first ones to die, imo.
Even tho I have a theory based on Nick's "I might go back to film more episodes soon" comment.
It's obvious they're listed with the cast because their names are being used for promo.
Look at AHS for an example. Patti LaBelle was named on the Freak Show poster despite appearing in 4 episodes. Patti LuPone was listed on Coven's poster despite also being in 4 episodes. Chloe Sevigny actually appeared on the poster for Asylum despite how little her character mattered.
Shows are always gonna milk their biggest stars, and that includes Nick & Ariana because of their demographic appeal.