Yes, sacramentals keep their blessing so long as they retain their form, which is why the prescribed method for disposal is burning (for those sacramentals that can be burned) or breaking up into small pieces (for those sacramentals that can’t be burned) and then burial. As for blessed palms, before burning your collection yourself, you can also call other nearby parishes to see if they are going to have a palm collection for Ash Wednesday. If they are interested in your palms, you can take the collection in and the parish will do the burning.
