You can have the soft as a portable app on a USB key. That's what I do. The best could be to have a 100% offline version without having to log in.
An online version is, from my point of view, the worst thing that could exist: The company disapear then the app disappear with it.
Chuck Dee commented
This is what makes me continue to go back to dabble (https://www.dabblewriter.com).
This app so needs an online version. What if I am traveling through Tibet and finally get to a computer and MUST download the app. No, I say have an online version, where the website becomes the writing suite.