Basically, you're asking, "How sturdy are circular needles?" or perhaps, "How well will these stand up to a bit of rough usage?"
The answer is, it depends.
It depends somewhat on the brand...but even individual needles vary in their sturdiness, so the best answer is that you will figure it out for yourself.
It pays to check the joins periodically. I have had one come apart, and it isn't fun! But generally, they will hold up to the normal "wear and tear" of normal knitting.
How's that for ambiguous?