I wanna ask that if there is no new post (content) in for example a month, does that reduce my overal CPC

Why would it?

I have sites from before AdSense was launched with very little change to them, the biggest change for all of them was going mobile/responsive a few years back, the information on them is evergreen and apart from occasionally changing to better images, essentially no changes.

The biggest issue all of us have is in retaining Google love irregardless of how good your content and information.

No one knows how to cultivate Google love unless one is their next door neighbour or has a huge pond of investor money all with the right connections, however if you are doing ok now under current Google algos then you having a holiday from them ought not to have much/any impact.

Thanks RedBar for your reply. So basically you want to say that this won't reduce nor affect to my overall CPC if I still keep the same quality traffic to my old posts right?

I don't think it can be guaranteed either way. Google is a fickle beast, whether it's search or Adsense. You'll just have to see how it unfolds for you by keeping regular track of the numbers.

I think uniqueness is still valued but number of words? Bah. Some would have you believe that there is a "magic number" of words to use. I've seen skimpy pages out-perform mid-to-heavy ones, ones that I would judge "better, more quality content". Google judges content like an American Idol judge.

As CommandDork says, nothing can be guaranteed, however if your quality and relevancy is high I would see no problem so long as visitors keep on clicking.