Not as long as I would like, usually!
Aside from essentials like asking for things in shops or on the bus, I can go pretty much indefinitely as far as I know - several months isn't unusual. I've lost touch with my immediate family for anything up to five or six years several times without it ever being caused by falling out with anyone. I don't go out of my way to avoid people, and I have times where I can be quite sociable, but I don't pressure myself to socialise if I don't feel like it, and it's not something I would think to do unless someone else gets the ball rolling.
_________________
When you are fighting an invisible monster, first throw a bucket of paint over it.