Multipage on yii2 + reactJs?

Question

React

There is a yii2 backend that generates html itself, an ordinary old site - site.ru
It has a rest api - api.site.ru

For the sake of practice, I want to transfer site.ru completely to react, but in some places I don’t understand how to build the work, namely:

1 I have to give the same statics with one bundle from any site.ru page, and use react-router for multipage, right?

2. How to handle 404 ?
- I understand that react-router has the ability to catch all "routes not specified", but what if my fetch request returned 404 ?
Do I understand correctly that this is solved - by throwing an exception, and by react to catch it?

thanks for the help