An interesting question which I personally have not given much thought to.

My observations would be this.  Battery disconnection for several days
is often quite likely to happen when a vehicle is in the garage for
extended service. With any disconnection of an hour or more then systems
without non volatile storage will lose their settings.

I recently fitted a tow-bar to my Croma (2005) and had the battery
disconnected overnight.  I lost the clock and the electric window
anti-pinch settings.  The windows through a warning triangle on the dash
but this was cleared by me taking the windows through their 'reset cycle'.

Also many car dealer show rooms have vehicles in there for weeks and
sometime months on end.  In every dealer I've ever visited these
vehicles have tier batteries disconnected.

I personally would be tempted to do a trial battery disconnect for 24
hours and see what I have to reset etc...  Then do it for a week.  Then
a month.  If there are any issues then this should show them up.

To me, logically once a car is without power then all knowledge of time
is lost so why a day, week, month or year should make any difference  I
 don't know.

Suggest that if you are going to give the power disconnection for
varying periods a trial then do it when you know you have a few days of
recovery time should you have to visit your dealer.

Your only other option is to use a 'battery saver' charger.  These can
be mains or sun powered.

Nick /////