When you want to un-install any AppExchange product or package, the process involves following a set of steps to ensure that no components outside the package are referencing the components in the package or vice versa.
Following the steps will help in un-installing a Package to remove all the components that were installed as a part of the package. Here are the verifications to be performed.
The above list is not an exhaustive list. Based on the package, the components will differ. Keep a copy of the data export file Salesforce automatically sends after the un-installation for future reference.