Cowardice within a game is frankly so ridiculous that I find myself without breath due to sheer pity and hilarity... If someone has fear over a game, my advice is that they give up on the world in general.
Who, may I ask, wishes to 'escape' from a nuke? There is no fear involved, there is concern, granted, but never pure terror. Without said fear there is no option for cowardice.
For example, I have abandoned tribes to increase my chances of survival, I have not done this through fear, I have never been ashamed of losing, I have done it for my own interests, pure and simple. If this is deemed cowardice, you might as well deem yourself a coward every time you improve your account.
As for deleting, I suspect they were just cutting their time consumption, having seen what KnK have done to other players such as themselves. Foolishness, maybe, but cowardice? Not by any stretch of the imagination. Sometimes attacks just finish off any love you have for the world, I know when I quit, I had been semi-active for a good 2-3 months beforehand, when the attacks rolled in, I found it took too much time from my other commitments to bother with, especially with this being a dead world.
There are likely many factors here that we will simply never know, but I wouldn't deem someone a coward over a game - yes, it's a game, something some people are keen to forget - even knowing every fact, which we don't.
As Serpico said - 'We are not enemies, we are opponents', much like a game of Chess. I've never seen someone called, or been worthy of being called a coward during a game of Chess. Such petty and shallow insults are unwelcome within a gaming community anyway, it never hurts to be civil.