Injured player

[sm_bbcoach]

YOu determine the outcome:

Player A3 hits a home run over the left field fence. As he is rounding second base, he slips on the bag, tears his ACL and can not walk/run. He is taken out on a streatcher.

1. Is Team A allowed to replace the batter/runner during the play, to finish the home run "trot"?

2. At what point is the play dead to allow a replacement runner.

3. What if A4 was on first base, and he is the runner who becomes injured during the home run by A3. At what point can he be replaced?