No flights home - emergency visa extension?

Visitors from countries that are visa exempt like Canada, America, UK cannot get visitor visa emergency extensions. Visitor visa extensions only apply to visa holders of countries that require a visa to get into Japan in the first place like China, Vietnam etc. A weird irony.

Since there is a state of emergency and no flights back, how likely is it that immigration will extend my visitors visa?

According to Skyscanner, there seem to be still many flights.
"A bit more expensive compared to usual" wouldn't be a good reason for "mergency extensions".

If there is "no flight," then the following would apply to you.

If you are from one of the temporary visitor visa waiver countries, upon entry into Japan you are given a gTemporary Visitorh status (stamped right into your passport). So that is the gstatus of residenceh that you have currently, with a validity date.

This page gives you info about how that is handled currently:
http://www.moj.go.jp/content/001316300.pdf

It is from this page, which I recommend you check for any updates
http://www.moj.go.jp/EN/nyuukokukanri/kouhou/m_nyuukokukanri01_00003.h...