Q: What happens if you unblock a number again?

The article linked does not address your specific question, and is not entirely accurate.

Voicemail messages from blocked numbers  appear as "blocked messages" and still can be listened to.  Unblocking the number doesn't change the status as "blocked messages"

Text messages (SMS, MMS, iMessage) from blocked contacts (numbers or email addresses) do not appear anywhere on your device. Unblocking the contact does NOT show any messages sent to you when it was blocked.

Do you know what happens on the blocked number's end?  Do the messages bounce back to them, or just appear to go through?  I can't seem to find that info anywhere.

I tested it out by blocking my sister, and seeing what happens. Calls go through as if they're ignored, text messages go through with no indication, and iMessages are the same. Facetimes come up as unavailiable.

Regards, C