The N3V DLC assets are replacable, as they are listed in your N3V account.
Assets like the NKP Berkshire are automatically installed in your game, when you start it ... I am unsure if you can back them up on an external hard drive, or not.
All your favorite 3rd party assets, and all your routes are in the Userdata folder.
The Userdata folder (and possibly another folder IDK) can be saved on an external hard drive (that costs @ $40 - $80).
Backing up some irreplaceable assets on an external hard drive is a good idea, because one never knows when a PC will go south, and fail.
I have an external hard drive, and created a folder which I named: "Downloads).
Whenever I go to a 3rd party site I download an asset, I click "Save" and that CDP I direct to my PC Downloads folder.
When my PC Downloads folder is becoming huge, with a thousand CDP's ... I regularly send them all over to my External Hard Drive - Downloads folder.
There is nothing that says that yor external hard drive can't go bad someday ... but that's PC life.
I always take my very favorite routes and assets, in the CM by, clicking each one individually: "Save As CDP" in my PC Downloads folder, which eventually all get sent to my External Hard Drive - Downloads folder.
If you have your Userdata folder backedup on an external hard drive ... If your PC ever failed, or a patch failed ... You could reinstall the game and start over again ... by deleting the factory Userdata folder, and pasting the "Saved Userdata folder in its empty place.
Never cancel a patch, if it seems stalled like 16 hours, it usually is doing something silently.
If yoiu cancel a patch, you must uninstall Trainz, and reinstall, starting over from scratch.
Your antivirus must be temporarilly turned off while installing Trainz, and while patching.
It is best to install a patch overnight while you are sleeping, as you can not sit and watch it patch ... Go to school, or work, and maybe your patch will be completed when you get home 8-16 hours later ... some patch's only take a few hours though.
When you installed Trainz for the first time... What build numeral was displayed down in the corner of your screen ???