So what happens to the blockchain when POW ends soon? There are no Prime Controllers or Orion nodes to control the network and record transactions. They are supposed to handle transactions and mint coins when needed. If there are no miners and these parts of the infrastructure are not online the blockchain will stop growing and transactions and trades will become impossible to perform.
Actually according to the timeline, the prime controllers were already created on Monday the 15th. So they are already out there.
http://www.tiki-toki.com/timeline/entry/376190/GAW-Timeline/Are you sure? Any evidence of that in the source code? Or how else is that going to work?
Yes, read sections 5.4.2 and 6 of the white paper. Prime Controllers don't have anything to do until POS starts.
But when POS starts, the nearest prime controller to the transmitting node verifies and locks the transaction, then broadcasts it to other nodes and controllers. If a consensus of prime controllers agree that it is a valid transaction it gets added to the blockchain.
The weight (number/quantity) of the staked coins that prime controllers have give them more authority to verify. The weight of the staked coins also disincentive-izes the prime controllers (or a consortium of prime controller owners) from performing illicit transactions.