The Apishield trapping cassette is removable so you can choose what you want to do with the wasps - I have seen videos of a French beekeeper running a blow-torch through the mesh before opening the cassette - seems a bit gruesome, not to mention the risk of setting it on fire. I leave them, they dehydrate very quickly and die off plus any live wasps are themselves an attractant to other wasps. If you wanted to, you could put the cassette in a bag and then put it in the freezer!
Note that I do not use the Apishield as it is intended i.e. as a replacement floor. For a number of reasons I think it unsuitable for that and so I put it under the OMF and seal the back of the OMF with a fine mesh - Apishield still works and it relieves the pressure on the bees of wasps trying to sneak in the entrance.