you cannot switch ON that network without declaring yourself a miner!
You can have a non-mining node. Not everyone has to be a miner. It was planned from the very beginning.
The current system where every user is a network node is not the intended configuration for large scale. That would be like every Usenet user runs their own NNTP server. The design supports letting users just be users. The more burden it is to run a node, the fewer nodes there will be. Those few nodes will be big server farms. The rest will be client nodes that only do transactions and don't generate.
i wonder what will happen when the official coins are mined in full
Then, the system will switch entirely into transaction fees, and nothing else. Then, 21 million coins will change hands, but there should be no new ones being generated, all of them should be only reassigned, when it comes to ownership. Also, we have a separate topic about fees, you can read it too:
https://bitcointalk.org/index.php?topic=5465318.0