12 Things You Learn Rewatching Avengers: Endgame
3. Nebula Knew Someone Wasn't Coming Home
There must have been some difficult discussions when it came to teaming up in the time heist, and where each team would go. Some, like Cap grabbing the sceptre from Rumlow, seem more obvious than others, but it's the off-world jobs that could have been the most debated.
In the end, it was Natasha and Clint that were sent to Vormir after the Soul Stone, which is really quite lucky. The two had a strong relationship and most certainly loved each other, so the sacrifice was real. However, if for example Rocket and Thor were sent to Vormir, since neither loved the other they would not be able to make the everlasting exchange.
Nebula must have had some impact on this decision. She knew all about Vormir, and obviously knew what was required to get the stone. In Infinity War she pieced together what Thanos had done and how he obtained the gem, and so she knew what was needed of either Clint or Natasha.
However, she clearly kept that information to herself, as neither were expecting such a revelation when the Red Skull told them. This version of Nebula didn't return to Avengers HQ at the same time as everyone else, which, unless she was very good at acting surprised when one of them didn't return, may have been a good thing.