TLDR: Kicking you is perhaps a little far but its pretty much what happens if you aren't showing up to raids ect... Also as someone else pointed out, high school really is a breeze, seriously, one day you will look back and be like man I wish I could go back and bludge in high school again... I know I already do (im 26 now) University is much more full on workload that will require you to be doing hours of homework pretty much everyday in order to get good grades.
Anyways, honestly man I wouldn't get so offended that your kicked from the guild if you really want to experience the game (in my opinion) being in such an elitist guild is the wrong way to go about it, the most fun I ever had on WoW was being in a more relaxed guild where everyone was very social and got along well, you looked forward to logging in to catch up with friends instead of just logging in for some ipoints. These kinds of guilds can still progress very well, my guild did most current content (including hardmodes) for 3 xpacs while being a casual guild.