Once again, no. Your antivirus companies might want you to think that it requires magical tools to kill a virus (and it does a lot of the time, which I'll get to) but not always. To "restart itself" it has to be running in some fashion somehow, which really means it hasn't even ended. Whether it's in your memory or a file or whatever doesn't matter - because if it's in any of those, it's pretty much guarenteed to be running and it isn't stopped. Viruses that 'infect' in some way don't even have processes in the "hello, i'm virus.exe in your task manager" sense. They are embedded in the OS, kernel, files etc.

As far as I know, ishost.exe is pretty amateur and doesn't know how to infect files so it can 'run alongside'. At some point you had to actually run some program that had it. So when you kill it's process it isn't going to automatically reload itself because it's stopped - unless it's in your startup directory or there's another virus (which does happen) that will download it and run it again free of charge. Then it's a problem. To say it never stops a virus from working - although like you say it's a pathetic virus that does when you end the process - is just plain wrong. You could call a virus that runs in an .exe more like spyware or whatever, but what's the difference?