To clear up the confusion which seemed to exist - No, the other Hanabi Festival games are not gone. The Lost Levels is the only game that was available for a limited time. This means you can still download Mario's Super Picross, Ninja JaJaMaru-kun, Ninja Gaiden, Gradius III and Sin and Punishment.

If you've downloaded The Lost Levels, naturally, you get to keep it. If you delete it, you can still redownload it in the Shop - The game page can not, however, be found in the normal lists - You must access it from your "Games You've Downloaded" list.