Leaving Japan, NEED advice. Can I hand in Moving out form by email?

I was working at EXPO, so I am a registered resident + registered for Health insurance. My flight from Japan is early in the day this Monday (1st). I made a mistake in my schedule and didn't realize the Ward office wouldn't be open on a weekend so I can't go hand in my documents in real time.

My question are:

1) Can I hand in the documents online/alternatively to do things properly and in advance? What is the best way to handle this?

2) Is it better for me to pay for my insurance for September as well or should I leave it by paying only for August? Will I be fined for not cancelling the kokuho?

I'd like to come back to Japan again for Working holiday Visa, so I want to do this properly if I can.

by myeyeswentdark