Illegal bat

[Antonella]

Italian softball umpires are discussing about this:

R1 on first base. No outs.
B1 at bat with a BASEBALL bat (i.e. an illegal bat) hit a grounder that F4 plays on 2nd, retiring R1.
B1 is now safe at first.
Defensive coach appeals the umpire about the illegal bat.
Of course B1 is out and the illegal bat is removed from the game.

Now the question is:
Do the other out (on R1) stand? Or the ump should better send back the runner on first base?

We discuss among us about this and decided we can rule this situation accordingly to the Batting Out of Order Rule. So that the play/out stands.

Do you agree with this? Or we'd better send back the runner on first?

Thanks in advance for every hint/suggestion.

A.

VERY IMPORTANT: In Italy the only Rule Book we use is ISF one.