Jetpack connection package: How to handle disconnecting from Jetpack?

Adding this for visibility and discussion in the open. The Jetpack Connection Task Force kickoff meeting has prompted some discussion about this.

In a future where a third-party plugin is connected to wp.com using the Jetpack connection package, how do we handle the user disconnecting said connection?

- If said plugin is disconnected, that shouldn't affect the Jetpack connection or other Jetpack-connection-powered plugins, I think we can all agree on that.
- If both the plugin and Jetpack are installed, and the user explicitly disconnects Jetpack, should the plugin's connection also be severed?
- If yes, we should add a filter to [this modal](https://github.com/Automattic/jetpack/pull/13517) so we can present the user with more reasons why he shouldn't disconnect.
- If no, then that means that disconnecting Jetpack won't affect the rest of the Jetpack-connection-based plugins. So, the site will only be truly disconnected from Jetpack when the last Jetpack-connection-powered plugin is disconnected?