Hypothetically, if miner profits went into freefall, the alternatives would be to raise tx fees even further (making the network less usable), or to change the

Hypothetically, if miner profits went into freefall, the alternatives would be to raise tx fees even further (making the network less usable), or to change the protocol to mint more coins. You are correct that the latter would massively discredit the project's original goals, and is therefore unlikely (since it would damage the value of the currency). The network relies on having a large ecosystem of miners to prevent anyone from mounting coordination attacks. Those miners are paid either by new bitcoins (out of the finite supply), or by tx fees.