Hey man... hate to burst your bubble but if WoW is still popular it won't end at level 100. Ghostcrawler commented on a thread and said this "Consider 100 to be just a number!" and also if WoW was to end at a certain level it would be 120 because 60 is WoW's halfway mark whereas Rift's halfway mark was 50. So basically WoW isn't ending at level 100 they could go all the way to level 300 and just continue to squish items down like they were planning to do in MoP orignally!
Anyways now onto the Old Gods topic! So there are five KNOWN Old Gods! The word KNOWN cannot be streched enough! There could be 7,9 or 10! We don't know although I do agree with someone who said these aren't the only Old Gods... the Old Gods could be in the millions and could be on almost every planet in the Warcraft universe the truth is we just don't know. I do see the Mantid being Old God related! Although anyone saying the Sha aren't a manifestation of the Old Gods are fooling themselves. The Old God's are like the Horde Prime of WoW. They are the biggest and baddest guys in the Universe! I mean if they whisper to people and make them go crazy! Sha are formed from negative thoughts... the Old Gods whisper to you so you think negatively and do evil... so although the Sha are not directly created by the Old God's they could be a result of something the Old God's do! The Sha are supposedly created by the last Pandaren emporer; for arguments sake lets say he started creating loads and loads of them... but he travelled to the spirit world to imprison them... Since he was the gatekeeper and is no longer around I imagine in the event of something crazy happening "The Shattering" that this would be enough doubt for the Sha to be released once again! All part of N'Zoth's play. Just because the last Pandaren emporer defeated the Sha that DOESN'T mean he destroyed them! The Titans defeated the Old God's but hey... look who's back?