If the V4 is anything like the V3, than there will be some
permanent souveigniers, but most of them are only temporary. The really expensive ones like plane ticket souveigniers (do you have those on the V4?) and the ones you get on the site that require a lot of effort, such as the V3 Golden Tamagotchi, will stay forever. I got them back around G2 and I still have them all on G18. Hope it helps!