So the foolish pilot flies too long, and the battery runs down. Enter autorotation, and it recharges the battery on the way down. By the time you get to the bottom to flare, you've got power again! I like the idea!
It will probably be happily difficult to over rev, with the clutch not engaged. I do wonder about type certifying an electric motor as a powerplant though! It looks like we'd need a whole new certification basis for that....