Will MacBook be re-added to Find My?
I have lost my MacBook. I went onto Find My on another Mac and it was offline. Accidentally, I removed the device from the Sidebar and saw the following popup, again I accidentally clicked "Remove".
Will this Mac reappear in Find My when it connects to the Internet?
No, you have permanently unlinked the machine from your AppleID. Your account would have to be manually re-enabled on the MacBook.