I have a similar problem with my FP1 first batch, the power button stopped working altogether this morning, I did not do anything special to the phone (no fall, nothing that I can think of).
To lock and unlock, if you use the F-Droid app store, you can use WaveUp as a partial workaround:
WaveUp (Turn the display on by waving) - https://f-droid.org/app/com.jarsilio.android.waveup
It allows you to lock and unlock your phone by using the proximity sensor (you can sort of see the little circle to the left of the top speaker). It works surprisingly well and has features to also unlock when you take the phone out of your pocket, and lock after the sensor is covered for a second.
It is a partial workaround as it does not allow you to use the power button shortcuts, and does not turn the phone off and on.
I will look into the option listed here and will let you know how I go.
What does it take to micro solder? Do you need a different soldering iron, and a different solder wire material?
Update: … and the button works again after 9 days of using WaveUp as a workaround. No idea how that happened. It is really surprising as it really seemed the hardware was gone forever, all of a sudden. Now it works completely fine, all the time.