If someone modified their SCA source files, and then lost their code, and there aren't any backups in the file cabinet, how can a copy of what's in production be obtained? (It's not me who lost it, lol)

Extension/Theme use fetch but for Core (SCA), mmm... I don't think it's possible.. It's either you revert to the version that's available right now and re-do all customization. Damn so sorry what you're going to get through.. Curios on what you'll figure out.

There is no way to get something like that. Last resource I would use is to go to the file cabinet, download the ssp_libraries for the backend custom modules and there might be a minified file for the front-end as well somewhere there, then the developer would need to recreate the custom modules one by one, just joining the front-end with the back-end in each custom module. Oh wait, I just re-read it, you said it is the source code, the approach would be similar, you need the exact .zip file with the original source code and then if you want to keep taking the bad decision to modify the core, inject the necessary code, otherwise is a good opportunity to create custom modules and create the repo for it.

Even with backup zipped uploaded and/or repo available on my end -- I still do check and confirm with the client who was the previous developer who touched/deployed to ensure I am using the up-to date version especially if the client went somewhere for other customization or even just went silent for a while. Ah! That feeling of deploying SuiteCommerce to the client environment after a long while! #FunTimes 🤣