The topic of this post is only an issue when you're adventuring in a 25 man dungeon. It's no problem at all for 5 or 10 man content. That's the problem with having large, tightly structured endgame adventuring groups. It's difficult to get the exact same people to log on at the exact same time so that you can all play this "game" together.

With a more flexible endgame adventuring structure, some imaginative gamesmithing, this wouldn't be such a problem. You DON'T HAVE to build encounters to make it difficult for players to assemble a successful group.

Just brainstorming alternatives, I can toss up several different ideas: Allow raids to hire NPC adventurers to fill empty raid slots; Allow understrength raids to fight bosses to a draw rather than a death, resulting in less loot; Split endgame raids into teams to accomplish specific lesser objectives racing against the clock or each other...

There are a LOT of gameplay innovations that could be used and developed to the point of allowing a much more flexible schedule.