What model X5 do you have? BMW confirmed no engine damage with mine - the V8 engine is actually relatively tolerant to low oil pressure - provided it hasn't been run with the red oil light on, ie absolutely dry, there shouldn't be any damage. The Handbook states it is driveable for a few miles after the CHECK ENGINE OIL LEVEL message, but not after the red oilcan light appears - that is virtually nil oil present and you must stop immediately to avoid serious engine damage.