Game Situation: Runners Switch Positions

 
With one out and the score tied in the bottom of the last inning, R1 (on 1st base) advances to 2nd base on the batter's (B1) walk. The defense calls "time" to huddle to discuss the situation. When the umpire puts the ball back in play, the defense discovers that B1 and R1 have swapped positions on the bases -- so that a much faster B1 could score from 2nd base to win the game. What does the umpire do now?
 
a. B1 (standing on 2nd base) is declared out
b. R1 (standing on 1st base) is declared out
c. Both B1 and R1 are out
d. Neither runner is out, just return them to their proper bases
e. Hope your partner knows what to do
 
Call
While we will never likely see this play, the play illustrates two interesting base running rules (1. runners passing each other and 2. runners retreating to a base).
 
When the ball was put back in play, B1 had passed his teammate (R1) on the bases. When runners pass each other, the trailing runner is out (NF 8-4-2m), so B1 is out in this case.
 
When "time" was called, R1 had acquired 2nd base. After the ball is dead, a runner may not return to a previous base if he is on (or passed) the next base (NF 5-2-2b1). R1 can be declared out on proper appeal -- so R1 is out in this case.