Hi there,
I've seen that Visual Studio 2013 professional monthly subscription is compatible with Visual Studio Professional 2013 Update 5, but internet is needed in order to use in this way, so if there's no internet then you cannot use the software.
So, I prefer to have an code key to make sure permanent activation but I don't know whether microsoft is still offering code key for old Visual Studio Professional 2013.
I've gone to https://www.microsoft.com/es-es/d/visual-studio-professional-2019/dg7gmgf0f6q1?cid=msft_web_collection&activetab=pivot:overviewtab that sells code key for only Visual Studio Professional 2019... but I'm not sure whether this code key could be compatible for the other old Visual Studio Professional versions.
Regards,