If you melt a cart or it gets loose then you can throw it out. But before that you can wash and reuse and i recommend you try the blue foam cart stuffing when the white stuffing gets old and cranky. Buy precut blue foam for 510 carts cheap at strictlyejuice.com (75 cent for 10 pieces) - cheapest way to try the blue foam.
Attys eventually burn out or get weak especially if burned dry (makes them too hot) or allowed to get really dirty. I recommend having 3 attys - 2 to alternate - using one while cleaning the other, and one total spare. Every weekend my dirty attys (one for each of 2 PVs) get blown out then swished/soaked in alcohol (I use vodka in a little jar - can't get grain in PA - some use rubbing but don't ingest that!) I make sure the attys are then submerged with no air bubbles. I leave then overnight. next day I scoop alcohol through each to rinse out any dissolved stuff, shake out and lay to dry. Meanwhile, I have switched to the previous week's clean dry attys after priming them well with juice.