It depends on their Objective,
In Enies Lobby, They split up because of Keys to Robin's Cuffs,
In Thriller Bark, They split up cuz each one of Mysterious Four had to be Defeated for varying reasons,
In Skypiea, They split up cuz They were looking for Treasure,
For Final Arc, I think Oda gonna Create "Nine Problems" which are gonna make each SH go their Separate Way to solve them,
Similar to how Onigashima had various Problems (Including Flames, CP-0, Big Mom, Perospero, Ice Oni Virus, Flying Onigashima, Kanjuro/Bombs, Orochi going after Hiyori and Smile Users ruining multiple Duels).
I don't expect SHs to form Teams, each one will have their own Separate Sub-Plot, but there are gonna be other Major Characters around them.