RAAL tweeters won't work perfectly if torn...they won't work at all...no way to vibrate to create sound. You could try talking with seller since he was not 100% upfront (he did say about the tear). Depending on how paid, you may have recourse.
If you get the S1 to S2EX upgrade, you get everything needed -- woofer, tweeter, crossover.
If you get the S2 to S2EX kit, you get everything needed - woofer, crossover. No tweeter as S2 and S2EX have same.
So, if you want to upgrade to the EX, that would be the way I'd go. If you just want to replace the tweeters, you'll need to call Ascend. I'm pretty sure they'll sell you one. I blew one on my S2's awhile ago and was able to get a tweeter.
http://www.ascendacoustics.com/Merch..._Code=UPGRADES