The following contains major spoilers for Avengers: Infinity War. You probably don't want to read this until you've seen it.
Avengers: Infinity War promised to be a major game changer for several characters. Possibly the character who saw the greatest, and most important change was Zoe Saldana's Gamora. Now, the actress has revealed that she knew from fairly early on what would be happening to Gamora, and while she was certainly shocked by the decision, she understood its necessity from a storytelling standpoint. According to Saldana...
I learned very early on. The producers called me and they told me. And of course there's a shock to your system. I'm so grateful, this run has been amazing, but you're so not even ready for that. But then once some of the things were discussed, I understood that it just makes sense. In order for you to understand the degree of evil that lies within the core of Thanos, you have to circle in on his own children. So I completely understood. I loved being a part of this unforgettable journey.
Of all the twists and turns that characters take over the course of Avengers: Infinity War, Gamora's may have been the most shocking. She accompanies Thanos to the location of the Soul Stone, where the stone's guardian, surprisingly, the Red Skull, reveals that to obtain the stone one must sacrifice something they love. Gamora at first sees this as a victory, as she believes Thanos loves nothing. Unfortunately, while she might not see his feelings toward her as love, Thanos does, and that's enough to make his sacrifice of Gamora worthy of obtaining the Soul Stone.
The moment is key to the events of Avengers: Infinity War as it shows just how off the deep end Thanos really is, since he's willing to kill somebody he loves in order to achieve his goal.
Zoe Saldana seems to be mostly ok with moving on, she has plenty more work to do after all, though her comments to the L.A. Times certainly make it clear that she'll miss her days in the MCU.
While the idea that characters would die was certainly a possibility in Avengers: Infinity War, few people probably had Gamora very high in the deadpool. Guardians of the Galaxy Vol. 3 is one of the few Phase Four movies that we know is happening, and there was certainly an expectation that the core team of the first two films would be in the third.
While there's certainly a possibility that Avengers 4 could undo Gamora's death, it really feels like there will be a difference between those that died at the hands of the Infinity Gauntlet, and those that died via other means. It now feels that Guardians of the Galaxy Vol. 3 won't necessarily be the end of the original team, but instead the team dealing with the loss of one of its members.