Also, miners might start to supplement their income by hosting LN Nodes and getting fees from forwarding people's tx's. If they stop mining, then the Lightning Network will stop functioning and they will not get any fees from both the LN and the miners fees from their Bitcoin mining.
So in my opinion the Lightning Network actually supplement their income or it might just balance it out, when the Block reward decline.
I don't think if setting up Lightning Nodes will be profitable for them. Lightning Network earnings are quite small and might not be worth the hassle of balancing thousands of channels. If some miners decided to stop mining due to low profitability then the difficulty would drop resulting in higher profit for those who continued to mine. None second-layer solution will replace on-chain transactions. Miners will continue to earn from on-chain fees. What is more profitable for an average miner? Small blocks and spikes in transaction fees or big blocks and small fees?