I was wonder is there a way of stopping ppl leaving half way though game!
What do you want to do?
Chain them to their device?
Shut the door and dispose the key?
Mind you that this is a game, an online video game, and anybody can leave it at his discretion, whenever he wants!
There may be "legit" reasons or those we don't call legit, but civility and courtesy are not common to all - that's life!
You can only react to it. My suggestion is "block and forget"!