Synchronization: iMessages on Mac not iPad How to turn off iMessages on iPad but turn on them on Mac?

And If I turn it off on device, does sync happen after I turn it on?

Situation:
I have an iPad and Mac. 
I want to turn off iMessages on iPad, but turn it on on Mac.

Ok, I go to iMessages on iPad and turn it off.
But now I don't see that my messages are delivered on Mac.

And what will happen if I turn iMessages on iPad on? Does all data sync with Mac?
No, there will be no sync.
Only the devices, that are registered on iMessage at the point of time, when the message is sent by the sender, can receive the message (technically). The messages are end-to-end encrypted for each receiving device.
In other words: Your new device can't decrypt the old messages, as the original sender didn't know about this new device.  

See this article:


  You’ve actually got one set of keys for each device you add to iCloud,
  and each iMessage is encrypted independently for each device. So if
  you have two devices — say, an iPad and an iPhone — each message sent
  to you is actually encrypted (AES-128) and stored on Apple’s servers
  twice. Once for each device. When you pull down a message, it’s
  specifically encrypted for the device you’re on.


Apple's Security Paper