If spontaneous remission is super rare it does change the conclusion, yeah. (Tangentially I think your stats are a little messed up there - you calculated the

If spontaneous remission is super rare it does change the conclusion, yeah. (Tangentially I think your stats are a little messed up there - you calculated the expected number of people out of 43000 surviving, not the trials returning a false positive. Assuming 0.0016% that chance is astronomically small, so your argument is stronger.)