OK, dealing with the one by one...
1) No, Huang Zhong didn't get killed. He ran like a coward. =P
2) Hm, neither Liu Bei nor Sun Quan were at that battle either. By your logic, they are also cowards. Do the words "away on other business" mean anything to you? =P
3) It was Wu who opposed the alliance, if memory serves. Lu Meng and Sun Quan wanted to take back Jingzhou, which Guan Yu had refused to give them, despite the fact Liu Bei had already agreed to it in return for their help and Chi Bi.
4) Surgery was dangerous in those days. Not wanting to be operated on was understandable.
5) Hm, I'm not sure how accurate your version of the Zuo Ci affair is, but what I do know is that he was rather insolent towards Cao Cao, and did say something about "helping Liu Bei". So really, Cao Cao's suspicions were fairly justified. As for him being scared of Zuo Ci, well, the guy was a mystic. He vanished into thin air when Cao Cao tried to have him executed, according to one account.
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Signature credited to Nathan (or whatever he decides to call himself next)MSN address: yamiken (at) hotmail (dot) co (dot) uk
[size=6](You know the drill, remove the spaces, replace the at with @ and the dot