Cards that aren't creature cards won't be returned to the battlefield, even if an effect made those cards creatures when they were last on the battlefield.

Creature spells that were countered never entered the battlefield, so Thrilling Encore won't return them to the battlefield.

In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, all creatures put onto the battlefield with Thrilling Encore that you controlled but didn't own are exiled.