Isn't that why we all play? I fail to see how it's any different than someone choosing to play the solo-campaign.
Well, if you had noticed I provided a very reasonable solution to this, but as you insist on making it an issue all I can say is that this wouldn't be something new to total war, let alone gaming, things like that are part of the nature of playing with others. The best thing you can do (as we do now) is get to know the people you play with. I've experienced many many droppers in custom battles presumably not always due to connectivity issues, and even a few in hotseat campaigns (which is to be expected considering how long they can last) and it does not prevent me from having fun.