The answer is more based on your needs.
Typically you would always have a very high quality master, that can then be used to create what ever type of distribution you may need in the future.
If this is a video of your cat taking a swing at a fish bowl, that you want to share with your MeMa, perhaps you can justify not having a 4k master.
If this is something you are going to use down the road in a platform other than face book, perhaps a 4k master is justified.
I work in film, broadcast and corporate, and I always create a master. Even for a corporate that they only want to put on Vimeo… I can’t tell you how many times they come back, wanting to do changes, or turn it into a commercial, or something like that. If all I had was the vimeo copy, we would be in trouble.
Glenn