Be careful about making a file like that -- one where you have to write the entire contents back to disk when you update it even though you only modified the last line or so -- too large. You're definitely better off splitting to give you more chances at not losing everything in the event that it gets corrupted. But I guess proper backups would also take care of that.
The "safe save" protocols that editors usually use to write file contents are pretty good. I've never worried about this and I've never lost a file to a mis-save, not in decades.
I don't think it's a concern. And you need to make backups anyway.
Often the "single text file" organization method is used along with a source control system like git to synchronize the file between different devices. So that helps with the backup/recovery aspect too.
