Forum Thread
Auction.
Forum-Index → Help → Answered → Auction.Hello Alien-Snowflake!
If your party and all your boxes are full, the Pokémon will be released after a while. It will stay 'on hold' for a limited amount of time, so you can make space, if needed, after winning an auction, but it's not for long. Can't seem to remember the exact amount of time, but I think something among the lines of an hour? After that time, however, the Pokémon will be deleted/released.