Just to be clear. Right now you can mine BetaNIM from our Betanet but these are for testing purposes only. The first NIM will come from the NET Tokens sold in the Token Sale. When we launch the final version of our Blockchain you will be able to mine real NIM and not BetaNIM. We plan to launch the Mainnet December 2017.
When NIM gets launched on December, what will happen to NET? which is currently trading at exchanges
Will it get auto convert like ANS ---> NEO
It can't get auto converted. NET Token is an ERC-20 Token which means it exists in the Ethereum Blockchain. NIM exists in the Nimiq Blockchain (which we are still developing, you can try the Beta version but the NIM are for testing purposes only). So in order to redeem NIM using NET, NET holders will use a web tool to receive a private key for a wallet in Nimiq Blockchain. This wallet will be hardcoded in the Genesis Block of the Nimiq Blockchain with the according NIM Balance (10 NET = 1 NIM)