[AP via CNN]:
South Dakota Sen. Tim Johnson has been exceeding expectations in his recovery from emergency brain surgery last week
The final point in the wire piece was that there exists ‘ample precedent for senators to continue to hold office while incapacitated’. Sen. Johnson’s successor would be appointed by Governor Mike Rounds. a Republican, so it’s safe to say that Sen. Johnson stepping down would swing control of the Senate back to Republicans [50-50 + Cheney].
I would think that Senator Johnson should stay in office as long as there is ample hope he will return.
He should serve for as long as he is able to meet the demands of the job.
As long as he is able to maintain the schedule and execute the duties he should remain in his seat.