Your Adobe Launch access should already be restricted to just people who need to be in there... not everyone with Analytics access should be added to Launch.
I suppose the risk of someone gaining access to the Launch Property would be the same as any system... if someone's credentials are hacked, someone could in theory have access to make malicious updates.
I don't know if the script itself could be hijacked.. but again, that risk would be the same as any other third party script I suppose...
If someone unauthorized did get access to someone's password, the same steps would be taken as any other site... go into the admin panel, remove access to launch (and any other Adobe products on the account), check the user's machine for malware or try to identify how their credentials were obtained, seal that up, change the password, re-grant them access.
Luckily there are logs and revision histories on the rules and data elements etc... if you are using the Adobe Servers to host the files and have , there is an option to turn on archives, which allow you to republish (up to 3) I think deployments back...
If you are self-hosting, I think you just have to create a build with your previous rule and element revisions and re-deploy. (archive doesn't seem to work for self-hosted.. at least not for us).
I don't know how you would detect issues or malicious changes... I think you would just have to monitor the deployments.
Or you could create a "deployment landing zone". Have the Launch deployments go to a separate server, then have a job that needs to be manually run to copy those files into your production site... this would require your devops team to have some manual steps for the process, but then, only properly requested changes would make it to your production site.