I can't honestly foresee a circumstance where there would be an all-out WW3.
Russia, China, and the U.S. know that if a global war started it would be Armageddon very quickly-- what used to be called Mutual Assured Destruction (MAD). All parties would be quickly annihilated due to each of their tremendous stockpile of nuclear weapons. I believe the U.S. has twice as many nukes as anyone else, but all major cities would be destroyed in the U.S. and everywhere else. The heads of state of the major counties know that, and will never allow themselves to be drawn into a massive WW3.
If Trump gets in the Russia/Ukraine war will end quickly. I don't know how wide the warring will get in the Middle East, but no superpower will get directly involved. A global WW3 is not going to happen.