XF 2.2 Display notice for user when some add-on uninstalls

[Kruzya]

I have a "core" add-on what provides a API for custom add-ons for registering own providers (implemented via table in DB, like connected providers and TFA). This providers implements some functions for communication between core and something services.
User can create a service in ACP and provide for custom add-on details like host address and port, where service is running.

Question - how we can automatically display notice about "existing related service"?
For understanding:

1. When add-on installs, he create My\AddOn:Protocol entity.
2. User manually creates My\AddOn:Server entity via ACP.
   When he do this, he should select My\AddOn:Protocol related entity for communicating core with this service.
3. User try uninstall add-on what provides a protocols and receive a notice about "requirement delete manually all required services", if we have something related with this add-on.

Or we should delete all related services automatically when protocol is deleted? What is "right way"?
I guess "notice" with blocking uninstallation before user deletes required related data - is more correct than auto-deleting.