I would make it so that the loot lockout applies to one single run and not just one piece of gear. Basically, you are locked out once you win 1 or more pieces of loot in a single run. So even if you get what you want on first chest, it would be worth staying for the entire run because you could still get more useful items in the next chests. Also, this would mitigate the problem of items simply being tossed aside since people might still roll for something moderately useful since there would be more chests remaining. Once you've won any loot and leave the run, completed or not, you are loot-locked out for the week.