Do they permanently go over? Do they disappear from my Platinum game?
It is pretty much migrating to the new games so yes you do permanently lose your pokemon to the new game.
In short:it is pretty much giving a pokemon to the new games(not trading)
How to change your username
How to add a user avatar
Why was my post hidden?
Flags vs Downvotes
Official PokemonDb League
Type a Pokemon name, type, move or ability to see instant results.