1. It is not a passive meaning, but a passive sentence structure. This sentence is not passive, because the subject (he) is doing the action of the verb (dying).
There is also a grammatical mistake: "He would have been dead"
2.Again, it is "He would have been dead yesterday"
The main difference is that in sentence 1, the subject (he) would have died yesterday, but in sentence 2, it means that he could have died yesterday or some time before yesterday. So for sentence 1 he can only have died yesterday but in sentence 2 he could have died before yesterday.
It is a bit complicated so I hope this helps. Feel free to ask me more questions.