Honestly, I think it'll be Tim Griffin. Sarah Sanders is a national figure at this point, and I think Arkansas will be more in the mood for a figure who's actually associated with their state. And if Trump loses he may not have that ability to move elections anymore.
In a state like Arkansas, he could still have clout. What puzzles me is why she seems fixated on Governor and not on the Senate. I definitely have Boozman down as a possible retirement and she's clearly more interested in national, not state, politics and issues.
I think she wants to run for governor because her dad is a former governor, not a former senator.
I think Leslie Rutledge (the Attorney General) has plans to run for the Senate if Boozman retires. She registered a website domain for a senate run last summer (or at least someone named Rutledge did).