Uhmm, maybe it depends on the phone? I backpacked Europe 4 years ago without a data plan and I have all my location history logged, it seems like it kept it on my phone while offline and then it uploaded it when connected, I used a Galaxy S5 btw.

I'd prefer it to be saved locally or sent to a server of mine with some standard protocol (maybe NMEA 0183 over HTTP POSTs) and never to Google. Of course I could write an app for that (and I did some 8 years ago) but it would be much easier if the OS would cooperate.

By the way, I disabled location services on my devices to prevent at least this form of spying on me.

OwnTracks is an app that does that, https://owntracks.org/ , but I still haven't set up my server to receive the data.

It uses MQTT, which is probably fault tolerant/store data locally if it can't connect to the server right now.