(This post is going to be pretty personal for the most part, but I will wrap it up with a final, general opinion in the end.)
Now, this seems like a pretty morbid topic. But right now my great aunt is in the hospital with an exploded intestine (I believe) and she was in a coma only yesterday. All of our famly members want to go visit her, but my cousin Carly is hesatant. Now here's my thoughts. I've been through more than one situation of choosing between whether seeing the dying relative or not, and it's never an easy decision. When my father died in 2003, my mom made the choice to not let me see him in the hospital before he actually died because she didn't want me to have that memory of him, as I was only 10. I am very glad that she did not let me visit, because that memory would've haunted the very few memories I have left of him only 7 years later. It hurts me that I didn't get to say a real goodbye, but I know I really wouldn't have wanted to. In December 2008 my grandfather was dying, but he lived in England. As we were both older, my mom left my brother and I to the decision. That was one of the hardest decisions of my life. Whether to say goodbye to a man who without his existance I would not exist, or to save myself from the pain of seeing him the way he was. Another factor was the idea of a family of 3 with a social security income flying to England spur-of-the-moment was not very good financially. In the end we chose not to go, which I actually regret looking back on it now. It's funny how different the situation was from my grandfather and my father. Another relative was my great-grandmother (mother of the great aunt who is in the hospital now). She was over 100 years old, and we all knew it was her time to die, as she had been slowly losing her mobility and conciousness in a short period of time. This time we went to visit her, and I do not regret it. However, I heard just today that my other cousins where there when she died, and that I would be afraid of.
In conclusion, it really depends on the person and the situation. My cousin Carly has hypochondriasis as well as anxiety, and therefore I do not believe, in most situations, it would be best for her to visit anyone. But even someone who is fine with seeing a certain dying relative may not be able to handle seeing every one. It really depends on age of both dying and visitor, relationship between the two, cause of hospitalization, and many other factors. So, in the end, one must think very hard about the situation and decide whether or not their decision might be regretted later. Because in this case, you don't get a second chance.