But how does it know if the final ACK is lost?
Because it didn't receive it within the timeout period. I know that's a "duh" answer, but that's exactly why these states and timeouts exist.
Will the passive closer resend the FIN
No. Not unless further packets arrive for that stream, and that would result in "RST" (reset) being sent.
The whole process is complicated state machine to execute an orderly shutdown despite the possibility of network failures. Networks break, links experience errors, links become saturated and have to drop packets, devices fail, etc. As an exercise, run the state tree for an active connection when one of the endpoints just disappears (eg. power failure.)
TL;DR That state tree is designed to handle every possible failure mode.