If he is still in intensive care, it is beginning to sound like he is brain dead.
The governor needs to replace him.
Will not happen. Far more infirm leaders have been in Congress - John Quincy Adams dropped dead after a vote in the House of Representatives. The only way this will occur is either Senator Johnson dies or resigns. The former is unlikely, the latter will be prevented at all costs.
Regards, Ivan
He can legally serve out his full term while in a coma.
He's in a chemically induced coma, and they claim they are bringing him out of it S L O W L Y.
The governor cannot unilaterally decide to replace him. Johnson must either be dead, or submit a resignation letter first. Ain't gonna happen. They can keep him 'alive' for years. Heck, he could remain in a coma and run for re-election, and maybe even win another six year term.