Stone does not decay, and so the tools of long ago have remained when even the bones of the men who made them have disappeared without trace.

（1）and可以省略吗？

【答】可以。省略后so 是连词，省略前so 是副词。

（2）为什么不是have been remained？

【答】remain 是不及物动词，不跟宾语，无被动语态。