'What If's' - don't count
They should count - anything else it luck. Did the pilots consider, discuss the options.
With Virgin making an approach, Jetstar should have held at 4100ft (in case Virgin went round). With Jetstar following Virgin on the approach and Virgin having gone round to 3100ft, when Jetstar went round Virgin should have climbed to 4100ft (to allow Jetstar to climb as per the published missed approach).