In fact it would violate the US Constitution to not allow a replacement to represent the state in the US Senate, because each state is guaranteed equal sufferage in the Senate.
Article V.The Congress, whenever two thirds of both Houses shall deem it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments, which, in either Case, shall be valid to all Intents and Purposes, as part of this Constitution, when ratified by the Legislatures of three fourths of the several States, or by Conventions in three fourths thereof, as the one or the other Mode of Ratification may be proposed by the Congress; Provided that no Amendment which may be made prior to the Year One thousand eight hundred and eight shall in any Manner affect the first and fourth Clauses in the Ninth Section of the first Article; and that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate.
49 democrats (-1 Johnson)
49 Republicans
1 Socialist (Vermont)
1 Independent - Leberman
Does this make the vote breakdonw 48 dems, 49 republicans. I realize the socialist and Lieberman will vote comm, I mean democrat. Is this the breakout on the actual vote as long as Senator Johnson is debilitated. If he cannot resume duties, the Republican Govenor of S.Dakotal makes the Senate turn Republican? No? Is this politically incorrect, or as Gretchen Wilson says 'politically uncorrect?"
But for a replacement to be named the seat has to be vacant. And unless Johnson resigns, is impeached and removed, or dies he will remain Senator even if he never opens his eyes again.