They might be shocked. Luffy has so many wild and dangerous adventures in his memories. His friends would probably be in awe of how much he has endured and how strong his will is.
The characters' reactions can be quite diverse. Chopper would be extremely worried and immediately start his medical examination. He'd be constantly checking Luffy's symptoms and trying different remedies. Nami would be worried too but also thinking about how this could affect their journey and the crew's safety. Zoro might seem nonchalant on the outside but would be secretly on high alert, ready to fight off any danger. Sanji would cook up all kinds of nutritious food to help Luffy get better.
Usopp might be inspired to be braver. When he watches Luffy's memories, he could see how Luffy fearlessly faces powerful enemies. This would make Usopp want to overcome his own cowardice and be more like Luffy. And Robin, she would gain more insights into Luffy's kind heart. She might see how Luffy has always been inclusive and accepting of everyone, which would make her feel even more at home in the crew.
Zoro would be deeply affected. He has sworn to follow Luffy and his death would be a huge blow. He might feel like he failed in his duty to protect the captain. He would likely become more withdrawn at first, but then focus on getting stronger to avenge Luffy if there was someone to blame for his death.