The old MacBook Pro that I had appears to be removed from the list of devices logged into my Apple ID. I was wondering if my messages will not come up on my old Mac if it is not connected to my Apple ID anymore correct?

So, yes. Your messages will not appear on any other device which is not logged into your Apple ID.

I don't fully understand your question, but does this help?

• If a device disappears from the list of devices connected to your Apple ID, it will reappear as and when you log into that device using the same Apple ID. If you no longer have the Mac, It won't reappear.
• All your devices should sync with all your other devices as long as they are all logged into the same Apple ID.