Leewan, depends on the failures, obviously many scenarios could happen. The fact is if you lose all three hydraulic systems completely on the A320 series, you are left only with differential thrust for control, then it would be up to the pilots to have a go at crashing in a 'controlled' manner I would think.
I was just pointing out unlike the B737 which can be flown without any hydraulic pressure (as per Rainboe above), the A320 has no flight controls functioning with no hydraulic systems functioning. Mechanical back-up on the bus is to do with complete flight control computer failures, any action on the trim wheel or rudder pedals would still be actuated using hydraulic pressure.
An interesting quirk on the A320 series is that the PTU (power transfer unit) that allows the green to pressurise the yellow system and vica versa can actually cause a dual hydraulic failure. An example would be you have a major failure in the green system, now the PTU is runnning flat out being driven by the yellow system trying to raise pressure in the green with no liquid to run against. Without fairly rapidly turning the PTU off manually, you could damage the PTU and overheat the yellow system. We had an aircrew notice about this exact scenario, basically saying if you loose green or yellow just after take off, don't take too long about doing the ECAM actions; in this rare case a simple single failure could cause a double failure without prompt flight crew actions.
Cheers.