The local storage can be redundant SSDs inside of a fire proof enclosure like the "black box" airplanes have. From all of the derailments I have seen in the news in the past few years, i don't think I have seed a locomotive being destroyed.

Batch upload at the rail yard would be probably a huge infrastructure project, especially in remote areas with shitty internet. You'd have to place access points all over the yard, run fiber back to a central point, and then have a large amount of bandwidth for a train to upload say 2 days worth of footage from multiple cameras in 1080-4k resolution in under whatever the time it takes them to switch their loads and leave the yard.

But again, none of that matters if NTSB doesn't do their job and actually download the footage when they have the chance. Any cloud / remote backup is going to have a retention window as well where they would delete footage.