I have 3 questions:
1.What should I do with the coins stored in my VXB wallet?
2.How should I handle the coins from previous mining that are still locked up?
3.If I bought NPT on SafeTrade and then withdrew it to my own wallet after block 23400, are these NPT tokens invalidated/voided?
You should export your secret seed phrase or your wallet.dat file, and your incoming_randomness.dat file. If you can only export your secret seed phrase, then import that into an instance of neptune-core and sync to the network – that exercise will populate your incoming_randomness.dat.
You will be able to redeem locked coins, although the time-lock will remain after redemption.
Consider transactions that took place after block 23400 void. I imagine SafeTrade will credit you with these coins since they will be able to redeem them.