You're missing the point of the article. To quote from the first line in that article:
There are several ways to move files inside Media Center. Doing so inside MC instead of using Explorer, for example, will allow MC to update its library to reflect the move.
By the way, if you google "jriver moving files to new hard drive" you will see this question has been asked many, many times before. Look at this:
https://tinyurl.com/11jyhzvmMC is a database. It knows where your media files are (at least the ones you have added to the library) and remembers that location.
If you "move, copy, paste" files in the finder, as you evidently are planning on doing, MC will not know you have done this. It will still remember your files at the previous location. So it will be wrong. And if you then add the files at the new location, they'll be listed in the database twice.
SO, the point of the article: Move the media files using MC (the Rename Move & Copy Files tool), instead of copy/paste in the finder, and MC will be able to update its library to reflect the move.
There is also method you can use that allows you to move the files using the finder, and then clean up the database afterwards in MC, but there are some settings you must adjust first (disabling Auto-import, setting FIX BROKEN LINKS=NO) otherwise you will have a disaster. So I recommend moving the files using MC if you can.
So I suggest you look again at that article, and read the one about the RMCF tool, and use that information to consider how you do your move.
Your question about what will happen in MC after you move your files is only relevant if you move your files using the Mac finder instead of MC. And if you do that, you will either have a small amount of cleanup to do, or a disaster. The outcomes you mentioned in your question are both possible outcomes, if you do it wrong. So you need to plan. Out of curiosity, how much (media) data do you need to move (# of files, and megabytes)?
Knowing how to move files isn't the same as knowing how to move files that are referenced in a database.
I hope this is more clear.