It's actually proven in episode 14 to 15 about what is going on regarding death in this case.
The basic idea is that, since Tsukasa's player is not connected to a terminal, it wouldn't work as simple as that. The player data is connected to the game in a different way, and thus doesn't use a "save" function.
Tsukasa is attacked in episode 14 by the guardian. The others meet up later and they had to reboot their systems to be able to do anything in the game again. They actually ask if Tsukasa remembers things that happened in the area, but he does not remember. It is established that his memory is linked to server memory in that case. Because it is linked to server memory, anything that had happened in the field that resulted in death in some fashion...
Simply took away the memories from where he went after he left the server.
So, simply put: Tsukasa wouldn't actually die in the real world if killed. Morganna wouldn't want to risk Aura being "born" in some fashion.