At some point, they will all be dead. There's no more Allspark to bring life to a dying Cybertron. there's no more sun destroyers to bring energy to a dying Cybertron. The Decepticons leave dying Cybertron and invade Earth to create a new Cybertron. The only way Prime can protect Earth is to use the 3rd Film's as yet seen McGuffin and end the life of EVERY transformer. Bay walks from franchise to direct other films, and the franchise will be ready for a reboot. Takers?