Generally speaking cloudshell is just a temporary type of environment and that should not be used by default across the Org for this kind of tasks unless the config files are stored - as they should be - on a private repository, being under GCP, GitHub, BitBucket etc.
Getting back now to your issue, I’d try to get all the details from that cloudshell instance by logging in and getting every information out of the “history” command.
With the output of history command you’ll be able to put together pieces of information that may help you to understand how everything was configured and managed by userA.
Gather all the files that you can find on that cloudshell instance (from userA) onto a directory and push them to a Git repository. At least you’ll have a copy of those files in case you need them until you manage to put all pieces together.
Your co-workers should install kubectl onto their laptops locally and manage Kubernetes from their machines instead of cloudshell, same for helm. Make sure all of them have the same level of access and visibility - this will help with the knowledge transfer later when userB and userC leaves the Org.
You mentioned about a 3rd party company that created helm charts / deployment process for you. If you’re still in contract with them or have a good relationship I’d write them and ask for a runbook / documentation of how the entire process works.
Either way you should be able to reverse engineer pretty much everything based on that cloudshell output and what you have actually deployed into your K8s cluster. I mean you can get everything you need just from your K8s cluster, deployment files, configmaps, secrets, ingresses etc.. Helm isn’t really doing any magic at all, it will deploy exactly the same files onto your K8s cluster.
“I suppose in reality the only thing we cannot figure out how to access/move from userA is the files and directories that customize the application to our organization.”
Just push to a git repo everything from that cloudhsell instance.
The App configuration (users, env vars etc.) should be present in the K8s configmaps. API keys, passwords should be all in K8s secrets. As for the image versions (app versions) those should be inside K8s deployments. All these can be exported and stored safely.