What occurs if R1 does not retouch second base on his way back to first for an uncaught foul?

When a foul ball is not caught, it is considered a dead-ball situation. This means that play is halted, and the defensive team cannot make any outs, including those related to base running such as a failure to retouch a base. In this scenario, R1 has the opportunity to return to first base without the risk of being called out for not retouching second base on his way back. The key aspect here is that since the ball is declared foul, R1's actions are moot in terms of being called out for not retouching bases, as the situation is no longer active, and he is allowed to reset and proceed with the next play after the dead ball is lifted.