retouch/appeals

[TriggerMN]

Example situation:

R1 on 1st, 1 out. Batter hits long fly ball to left field. R1 takes off and rounds 2nd base after touching. Ball is caught by left fielder. R1 then heads back to 1st base, but does not retouch 2nd. As R1 slides back into 1st base (touching the base), the relay throw gets away from the 1st baseman (the ball remains live). Then R1 advances to 2nd base. Play over.

Can R1 still be called out on appeal at 2nd base for not retouching? Now that he's standing on 2nd base, does that cancel any appeal? If the first baseman had thrown the ball to 2nd base, where the SS was waiting with a foot on the bag, would R1 have been out before he reached 2nd base?