Durable? Depends what's hitting it. Against any sort of bludgeoning it's great. Against slashing it's poor. Against piercing...well, probably also poor; though easier to repair than slashing. Against fire or acid, vulnerable. Against cold or sonic, no real problem. Standard against lightning. And so on.
Being knocked off it? Again, depends on circumstance - what's doing the knocking, and whether the riders are sitting, standing, prone, etc.; also how fast the carpet's moving and-or at what angle.
What I do rule is that if you try to fly one in conditions of high or gusty winds you're asking for trouble as the wind can easily catch and tip it, or even flip it.
Lan-"when a party I was DMing once tried to use a magic carpet in a full gale at sea it didn't end well...but it did end quickly"-efan