What started my thinking of this thread subject is that the Energica bikes seemed to me to have the best chassis and build quality of the three current most popular freeway-legal electric motorcycle models on the market in the U.S. Although I honestly don't know much about the quality of the LiveWire, but i am pretty sure that the Energica seems to have better build quality and engineering when compared with the Zero. To me it would be a shame should you have to retire your Energica if its batteries didn't last as long as the chassis components and couldn't be replaced at a reasonable cost.
It's a pretty safe bet that with only a low-4-digits number of e-motorcycles of any given make sold per year globally (at best), it's not going to be worth anyone's while to have any commercial replacement programs.
Some people will do it just for the hell of it, but it'll be more expensive than a new bike. Somewhat similar to how EV conversions of old cars aren't cost-effective, once you take in account the cost of the labor and the fact that you get a car which still has far inferior safety and non-drivetrain subsystems than a modern EV.
Zero are going to have to move to high-voltage batteries pretty soon anyway, to support CCS DC fast charging (if they don't they'll be stuck with commuting and unable to grow their market); once they do that, IMHO the older 100V battery system is going to be orphaned anyway.
Energica already only warranty their batteries for 3 years / 50K km, which is quite low (and for me is a sufficient reason not to buy one).