In theory a composite fuselage could be able to stretch enough to withstand the tearing apart that is seen with metals.
In theory that is. I don't know if we ever will see such a thing in flight.
Reason for this is that if you place the fibers in the correct angle to the air flow, the fibres can stretch pretty far without breaking. The limiting factors would be the properties of the resin and the true length of the fibre. This is related to what Volume said about making the composite softer to get more strength.
However, since decompression can happen anywhere there is no catch-all possibility regarding the fiber position relative to the air flow and thus it is very unlikely that we will ever see a decompression resistant fuselage. I'm guessing it would be possible for those boxes transporting cargo in some distant future though.
Afaik the boxes from the Lockerbie testing were metal and thus very heavy, that's why no airline wanted them. Composite cargo boxes would be much lighter.