You really should remove that baby orchid providing it has a few live roots that are a couple of inches long. You could put it in its own pot.
The longer it remains on the old bloom spike, the longer that it can negatively effect the health of, and the reblooming, of the mother plant.
Your mother plant needs to summon all of its strength into growing new leaves and roots in order for it to grow larger, healthier and produce more flowers. That baby robs the plant of that strength and that strength goes towards the baby.
It could prevent the Mother plant from blooming properly next season. There is a chance that it won't bloom at all.