If i was the director of Toy Story 4 this is how it would be.

Beginning,An evil army of Captain presidious would attack and hold captive each and every toy in the world,(they thought).

Middle,the underground (which was Buzzlightyear and friends) center of toys that Captain Presidious did not know about started breaking the toys out of the Captains army and eventually got caught.

End,The toys that escaped from the dungeon formed an army dug tunnels through the ground and eventually Captain Presidious and his army eventually got sent on rocket ships to mars and they all died.