Are video calls placed through FB messenger really private or safe? What is the probability that it could be sniffed or intercepted by hackers? Is Facebook recording the data or just meta data of the video calls? If so, for how long?
Like all other traffic going through facebook, it`s TLS encrypted, so sniffers would not be able to see the video.
I personally dont think that Facebook would store video calls because of limited resources, but always take these things with a pinch of precaution. If sharing sensitive data through video calls, try to look for an end-to-end encrypted service.
Storing metadata however, requries almost no space, so you can assume, they store at least a few things like who you called, for how long did you talk, timestamps, etc. It's just a few bytes of data, it takes nothing for them to store and information is power.
Nothing is safe. But it is always a question of how much effort needed to attack specific resource, and how much trust you give to people that hold the data and build software.
No need to be paranoid, but its healthy to ask yourself questions, like:
"How much privacy I would like to achieve?"
"Am I trust "Company" as company?"
"And what about sysadmin "Bob" and developer "Alice" in this company?" "How much my privacy important for me and how much money need someone to put to break into my privacy?" and so on..