There was a suggestion above somewhere that I think provides a GREAT solution without the need to create new mechanics, such as tickets, etc.
Every guild member has 5 battles/day for 6 days.
This comes out to 900 battles.
If the end of week calculation for points takes only the BEST 800 battles, then you effectively create a 3 person vacation window. (actually better than that, since 3 players out would be only 90 battles missed)
The Guild would obviously still need to ENCOURAGE members to play their daily battles, but if a few people need to miss for various reasons then, it will not AUTOMATICALLY deny top rewards to a guild because LIFE HAPPENED.
It was a very nice suggestion, that I think got completely overlooked in all the walls of text! 
EDIT: Searched for it and it was @Grundulum. Gotta give credit where credit is due!