Your example is awful. You literally just made it up, this already wouldn't happen anyway.
Murder the poor moron and take all his stuff every time he "griefs" you.
Look, I'm going to be straight with you. This has not presented any new information or concepts or caused me to think about any aspect of this issue in even a slightly new way. However, because your initial premise has a built in safety valve "It's not just this one example." You can come up with new scenarios until the end of time because "it's not just this one example."
Look buddy, there's no end to this conversation. "What about this? What about that? What if x, y, or z?" It's never going to end! I know that you think you're making a valid point, but let me clue you in on a little secret, okay. Nobody cares. Alright, nobody cares. Everything you're talking about, no one cares. Even the people who have commented so far do not actually care when it comes right down to it.
There is no catch all solution. There is no perfect game. You said it yourself. There's always going to be a loophole somewhere. Soooooooo......... what do you want? God descending from heaven with the "Anti-Griefer Patch" day one after release? That seems unlikely.
I'm going to say "Repeatedly and relentlessly murder the griefers and take all their stuff." You're going to say, "but what if they don't stop even if you're killing them all the time." Get together with friends and build walls, don't let the griefers in, do whatever you gotta do. Now you say, "What if the griefer gets together with other griefers and attack your wall?" Uuuggghhh... That's called gameplay. It's a bandit raid, okay. It's... it's gameplay, that's how it works.
No one cares about your hypotheticals or your speculative fears. Murder everyone who won't leave you alone. "But how can you murder a griefer if he hasn't committed any crimes. You can't make a law for everything." ... Uugghh... Well, if trespassing laws to keep people from being near you aren't enough then I guess you're just gonna have to never play COE because it's full of hypothetical griefers. I'm sorry the game didn't live up to your hypothetical speculative standards.
Alright, bottom line, we can't build the perfect anti-griefer mechanics BECAUSE GRIEFING DOESN'T EXIST, HA!