ECUs do not require battery power to maintain their base maps, it is the "learned" behaviour layered on top of the base map that is erased when you disconnect the battery and the ECU has to re-learn that (which is why your idle will be funny for a short time). You won't harm the engine at all. Memory-saver devices are usually for keeping things like headunit settings, clocks or security codes, so you don't have to reprogram your radio stations or reset the time every time you disconnect the battery.

 

Is this a serious post?

 

No. Your ECU uses non-volatile storage to store data. The only danger MIGHT be if it is left unplugged for many years, where that storage might start to experience bit rot.

 

Question #1, If the battery is completely dead for a very long time, will the engine settings get lost? Will the car be driven safely after I replace the dead battery with a new one?

If the battery is already dead enough that you’ve lost you radio presets than question #2 is moot.

 

The only thing I know that is "needed" after battery is disconnected is a steering zero point calibration. I think it is needed for lane tracing to work.
The procedure occording to the service manual, you do the following:
(a) Start the engine.
(b) Drive the vehicle straight ahead at 35 km/h (22 mph) or more for 5 seconds or more.
(c) Turn the engine switch off.

basically after installing the battery, go somewhere where you can get up to at least 25mph dead straight. I believe it will automatically recognize that you are driving straight probably based on the ABS sensors reporting equal speeds, and will auto calibrate the steering wheel angle sensor.

for the hatchback it also says to initialize back door lock but I don't seem to have downloaded that page back when I had TIS.

 

This is interesting. Will the car throw an error/warning if this calibration isn't performed? If not, that might explain why some people report issues with the LTA "ping-ponging"