Here's how I see it. You should probably have a swiping gesture to get back AND a button at all times. Facebook's method is not highly intuitive, sure it's not really hard, but it could be easier. Google does a good job with this.
When a user wants to get to a menu that is commonplace these days, they want to look for something, the "three horizontal lines" is what they are looking for. When they press it, it should stay available. At this point they can be 100% sure of how to escape the menu. If the button disappears, or you do something like Facebook, then for a while they could get irritated. You should keep the button, and perhaps add the swiping as well.
But when can I use swiping only?
In most cases, don't. However there are times when it could be useful. If you have it set up to be gesture oriented, and you make it clear that opening the menu requires swiping, then closing it with a swipe makes the most sense. This idea can be seen from the UX-loving Apple.
First, they teach you and expect most users to use swiping for their Notification Center.

Now, although you could use ONLY this approach, a much better UX is to ALSO do what Apple does.

Here, Apple adds a button as well, which is what I was talking about in my first point. You should have both. For desktop uses, you don't need to move this "active button", but on mobile devices, there really aren't many cases where you could put this button instead.
Conclusion: Almost always use the buttons, feel free to add swiping in addition, and don't allow the user to get back by having them touch a part of the screen that is implied to be "out of commission" like Facebook does. Tapping in particular, is not very realistic, and doesn't really make sense.
Hope this helps, if you have any other questions, let me know.