Oh, man, this thread is just sobering after looking through a few pages of this.
Echoing what Philip said a while back, most people tend to know and respect the friends you have in real life much more than the ones you would meet online, moreso if you are like me and use the computer at times where it is detrimental to daily life. I havent really made any friends here yet, but for SURE there have been some people here who have helped me out online almost from the start, thankfully none of which have died.
However, if someone dies on on online messaging board you are in and you become emotional about it, tbh some people would see you as kind of weird, since they are not really as tangible as friends that they can say hi to in person. Ex: say if I was on Bulbapedia boards and someone who had helped me out in the very beggining of my existence there had become really close, close enough to call a true 'friend', had gone up and died, I would sure be sad. The scary thing is that you wouldnt really know about this unless They had notified someone beforehand on say Facebook or even another member of the forums, who would then notify the general populace. It would just seem like they left the site. Nothing would seem odd about that if say they were new, but if they were a well respected member in the community, I think someone would take notice.
In my personal opinion, it is certainly possible to make a friend online which can rival and even surpass a friend which yo have made in your personal life, especially if you have more than one way of communicating and if you have a special connection in some way, if friendship wasnt already enough. You could, hypothetically, grieve them like you would a real friend.
The fact that my parents turned it on random zen music with a slightly Eastern twist to it helps to sober my mood right about now when I post this. However, dont get me wrong, I have never had any thoughts about going in my life, though I occasionally plan how I would leave my home and go somewhere far away, due to situations.