<p>Why dont you split the game into two modes, one where there are replacements for leaving players and one where there arent. The second could be used for competitive gaming and the first for casual. It should only require for an aditional queue and disabling the posibility of a player joining mid game. If you leave in the no replacement mode there should be a penalization though (ELO, time before you can play again in that mode, reputation, w/e).</p>
<p>Edit: you could use reputation to sort the queue making higher reputation players to be placed in-game faster. (just a thought)</p>
I used to play a MMORPG that had a mechanic similar to this but implemented in a different way called Argentum Online. Every player had a bank account where they could deposit items/money, This account was only accessed from a NPC in most cities. So you would go out to loot, if killed all the items you where carrying would be tossed on the floor but anything deposited on the bank would remain (you only had access to the banks items when alive and tacking to the banks NPC). They had a revival system where you had to walk to town and talk to a priest (your player transformed into a ghost when dead) and you wold come back to life(with no items though). There was also a revive magic that other players could use to revive you but since you dropped everything on death you usually lost most of your gear in the meantime. Some items couldn’t be lost though, mostly faction amour (this was obtained though a quest and couldn’t be bought so getting another one was impossible) but even the best faction amour was mid tier.
The bank account had no limit on money deposited but had a limit on items (it was an odd item cap, You could have up to 30 item stacks of 10000. this allowed to have tons of low value items like potions but restricted the expensive ones since having 10000 of any equipment was insanely expensive).