[Robert DeLong]

Not necessarily. It may fill with water like all the other splits have done in the past.

[deweyfrank]

I wonder if this would cause the ocean depths to recede, counteracting man made global warming? /s

[Axenolith]

The continents are primarily composed of granitic rock and the seafloors basalt, which is denser. The continents are essentially the lighter “foam scum” over a thick hot latte of the plastic mantle.

A “hot spot”, like under yellowstone or which the Hawaiian islands are derived from creates a triple ( 3 arm) junction in continental crust as seen here. If it matures 2 of the arms will become a sea floor spreading center and new ocean basin while the 3rd arm goes dormant. In this case the failed arm of the triple junction would be the Red Sea.