What are disconnected customers going to do? Surely they won't cut off the entire US military and DoD by terminating that cash cow of on premises.
Atlassian completely ignored the large number of smaller customers who are legally forced to use an on-premise solution. If the software industry was so hell-bent on SaaS there would be a great business oppotunity in creating an on-premise Jira competitor.
And it is the exact same software as Server with some extras enabled like support for multiple nodes, so upgrading to it is as simple as pasting in a new product key.
You’ve never actually had to update an on-premise JIRA instance yourself, I presume?