You’ll be backing up the visual with an IAP. With the exception of a few months of stupidity at one carrier, every operator has set the missed approach altitude for the IAP. 9/10 times, that’s the altitude ATC will give you on the missed.
You do NOT fly the “published missed” for the backup approach.
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*The few months of stupidity came from a desk pilot who thought setting 1500ft was smart. Theoretically correct, but practically stupid. If you go around in Boston, you won’t be told to join the pattern and report on base.