Valkyrie (odds of dying: 1,000 to 1)
Valkyrie (Tessa Thompson) has quickly become a vital member of the Thor franchise. She has also become popular enough to carry on even without the franchise in which she was introduced. We have only just met this character and there are so many possibilities for her, including that all-female team-up movie Thomson and friends pitched to Feige.
The only reason there’s a remote possibility she could die is if Marvel Studios underestimated just how popular she would become, wrote her demise into the Avengers films, and the moment is just too important to the story for Marvel to rewrite or reshoot it. We know that she is in immediate danger aboard the Asgardian refugee ship in the mid-credits scene in Thor: Ragnarok.
Bruce Banner (Mark Ruffalo) is also aboard that ship, though, and he makes it out alive since we see him on Earth in the trailer. The most likely scenario is that Loki (Tom Hiddleston) uses the Tesseract to help at least a few characters escape the attack from Thanos, and Valkyrie will be among them.
The Wasp (odds of dying: 1,000 to 1)
Evangeline Lilly is in Avengers 4 (she’s TBD for Infinity War), but she hasn’t been on set all that much. She did some work on the film while she was also in production on Ant-Man and the Wasp and still has more to go through the end of the year, but it sounds like her character may not play as big of a role in the Avengers movies as several other heroes. That might be a good thing, though, as a major character with a smaller role in the film is far less likely to meet his or her demise. She’ll be ready to carry on in the Ant-Man franchise, perhaps even leading it by herself.
Ant-Man (odds of dying: 500 to 1)
Like the Wasp, Ant-Man does not appear in the Avengers: Infinity War trailer. Those two characters might be in the Quantum Realm when all the fun with Thanos starts, which means Scott Lang can proceed directly to Avengers 4, where he will likely survive. He is one of the best at avoiding major physical harm and probably has a third film in his own franchise to make in Phase 4.
Not to be ignored, however, is the possibility that the franchise that has gone from Ant-Man to Ant-Man and the Wasp could simply go to The Wasp for its third installment. Scott Lang would certainly qualify as a truly shocking death that most would not expect, so we can’t completely rule it out.