Welcome to the dashcam world Rob.
If you want to be absolutely sure you can turn off the camera and take out the memory card, or replace it with a spare one if you are able to drive on after the event.
If it is a wifi camera you can stop recording and download the file / files with the event to your phone to make sure, but if it is a major event you will not be driving that car more today, in which place you should just turn off the camera and put the memory card in your pocket.
How long it take before it overwrite a not locked recording depend on size of a memory card and the resolution and bitrate of the video files, this should not be smaller than 64 GB for a single camera system.
Not sure you can change segment size in the nextbase cameras, but most do allow for this, choices are most often 1-2-3-5-10 minutes where i think 3 minutes are the most popular.
The regular files a dashcam record will be overwritten when the card fill up. starting with the oldest recordings on the memory card, if your camera are 1080p resolution and you have a 64GB memory card you will have something like the last 8 hours of driving on there before you start to loose the oldest recordings, so if it is just a little event and you can drive on you can do so just fine if you don't have too far to drive.
Locked event files i think now will also be overwritten when that memory space set aside for that fill up, but unless you drive your car like a bumper car and so trigger a lot of those events it will not be a problem as such.
In general i recommend to not use any form of sensors for events while driving, any little thing you can save manual by pressing event button, and if you have a major event and get knocked out, the first thing rescuers / bystanders should is turn off your car, and so stop recordings, and so your event should also be safe even if it is not locked.
And if you have a large enough memory card, you can drive off the road down to a ravine and be knocked out, and the car still running, but as long as someone find you within hours of your crash your footage of it should be just fine too.
The reason i recommend against using sensors while driving is:
1: the camera are recording all the time, so everything happening will be recorded anyway.
2: if not adjusted properly sensors ( G-sensor ) will trigger all the time, and so you can loose a event even if it is in a locked mode, if your camera delete old event files to make room for new ones.
If it do not recycle event recordings, you can risk filling the memory card up with those leaving no room for regular recordings, cuz in that case only you can delete event filed by formatting the memory card in the camera, or delete the files on the computer.
So the main thing is have a good sized memory card of a good quality
Look over your footage now and then cuz no camera really are set and forget, these few minutes spent every few months are well invested ( look for where drive sessions start and stop, that should be in familiar places like home / family / work / shopping / favorite gas station ASO )
If a recording start or stop in some weird place you might be having problems of some kind, just play the first few seconds of file you inspect just enough to register where it is, if you are like me you will probably find its the same places routes you go to over and over.
I take 5-10 minutes to look over a 128 GB memory card from my dual channel system ( on PC with the memory card in a card reader )
This include all first and last recordings in drive sessions from both cameras, and then i sample some random files too.
I only drive about 3 hours weekly so with a 128GB memory card even for 2 cameras in my system i still have well over a week of footage on my memory card.
You should not need to share anything on site of a crash, i would personally not mention my cameras to anyone so the other side have a chance to lie to police and insurance and so dig his own grave.
Just submit your footage to your insurance company, the one time i needed to do that ( for fun cuz other part took blame just fine ) i just uploaded the video to youtube as private, and then included the link to the video in my filings to the insurance company.
I think only if they need to go to court with the opposing insurance company will you need to provide the raw unedited video, and that's just fine too, by then you can put the raw unedited files on a CD / DVD or a small USB memory stick.
It might also be prudent to save some of the recordings leading up to the event, and that's fine too if your camera are 1080p resolution and record in 3 minute segments each file will be 350 - 400 MB in size, so you can fit many of those on a DVD or a cheap 4GB USB memory stick.
Rule of thumb is file size are about +100 MB for every minute of recording time.
Digital you can also share files over the internet using file share sites like googles G drive ( you get free if you have a gmail account ) Microsoft also have a similar free service, and there are file share sites like mega.nz too that will give you 40 GB of free online storage for free.
Its up to you and how comfortable you feel / are with this digital internet stuff.
