Some members might be shocked. Wonder Woman, for instance, who respects Batman's skills and tenacity, would likely be very disappointed. She might try to persuade him to stay, emphasizing the importance of his presence in the team. Superman, on the other hand, might initially be understanding, as he knows Batman has his own way of doing things. But he would also be concerned about the power vacuum that Batman's departure would create. Aquaman might be more indifferent, thinking that Batman was always an outsider to some extent, with his focus mainly on land - based issues.
The Flash might initially be in denial. He's used to Batman always having a plan and his death would be a huge shock. He would then turn his speed into a tool for investigation, trying to find out exactly what happened. Green Lantern could feel a sense of loss but also be spurred into action, using his ring to try and prevent future tragedies like Batman's death. He might create constructs in Batman's memory to inspire the team.
Some of them might be amused. They could find the different takes on their characters and stories quite entertaining. For example, Superman might chuckle at a fanfic that has him in a comical situation.
The Justice League as a whole would have a diverse range of reactions. Some members like the Flash would be all for it, seeing it as a fun exploration of Batman. Others like Wonder Woman might use it as a way to understand how the public perceives Batman's role in the League. And then there are those like Aquaman who might just shrug it off unless it directly affects his interests. The fanfiction could also potentially create some internal discussions within the League about how they are all portrayed in the public's imagination.
Some of them might laugh. They would see the creative and sometimes out - there ideas that fans come up with in the fanfiction. For example, if there's a fanfic where Oliver Queen teams up with a really strange character from the Arrowverse, it could be quite humorous to them.
In this fanfiction, Robin could be saving the Justice League from a threat that they didn't see coming. For example, a mind - controlling parasite that has infected some of the members. Robin, being the smart and resourceful character he is, figures out a way to neutralize the parasite. He might have to go through a series of challenges, like sneaking into a heavily guarded enemy base, decrypting complex codes to find the antidote, and then distributing it to the affected League members.
In a 'Justice League meets Robin' fanfiction, Robin could show off his amazing acrobatic skills to the Justice League members. They might be impressed and start to see his potential as a valuable addition to their team. Maybe Robin would help Batman communicate better with the other League members, as he often understands Batman's thinking.
They would be amazed. The Justice League is used to their own brand of super - powered battles, but Infinity War would show them a whole new level of cosmic warfare. Superman might be the first to jump into action, mentally preparing himself to take on Thanos if he was in that universe.
They'd likely be intrigued. Batman would study it for plot devices and character development. He might use some of the ideas in his own crime - fighting strategies. Superman would probably be entertained, seeing it as a new form of storytelling about a hero. Wonder Woman might view it as a cultural phenomenon and think about how it reflects on modern society's view of heroes.