No spoilers, but in the comics crossover event Captain America: Civil War is based on, Captain America gets killed. Wait, did we say no spoilers? Sorry. He obviously survived in the movie version, but his comics death isn't the only reason we don't expect Cap to make it out of Phase Three alive. While star Chris Evans has spoken publicly of his desire to continue working with Marvel, he's also been forthright about wanting to work behind the camera instead of in front of it—and as director Joe Russo told the Huffington Post, Cap setting down his shield at the end of Civil War should definitely be interpreted as the character "letting go of that identity."
Evans might be around for Phase Four, all right. He's just more likely to be directing Sebastian "Bucky" Stan (or Anthony "Falcon" Mackie) as the new Captain America. RIP in advance, Steve Rogers.