Even before... Trying to compile archived versions of the python 2.7 runtime on recent Linux distributions is an exercise in frustration. Thank god for the gentle souls that keep putting out lightly updated compilable 2.7 python runtimes, your efforts haven't gone unnoticed.
I have a directory full of prebuilt wheels for the entire dependency chains of several python applications I use. All you need to do is tell python to build all the wheels and save them to X directory, and point it back at that directory for installing.
In particular on Termux, there's a number of rarely-used python programs that have native dependencies, so I store them on my network drive to free up storage on my tablet. I have a similar setup for doing stuff on Colab.
It's entirely possible to use python/pip in an offline environment, as long as you've planned for it ahead of time; all you need is pip and possibly wheel, and the correct version of python.
Node predates npm. All node does is look for dependencies in the nearest node_modules directory. (And all npm does is download dependencies into that folder). So you can simply archive / check in your node_modules directory if you want to. I think there’s tools to help out and make sure the dependency versions are all pinned. (npm shrink-wrap and friends)
They already are, if something has been hijacked and is now malicious.
They already are, if you need to install something offline somewhere.
They already are.