You have the possibility to delete one or numerous participants. Here are the consequences in terms of the access restrictions to your application.
Your application is set as "Public" access
Even if you delete a participant, it doesn't matter. The user can re-authenticate with his/her initial account to access your application and retrieve all his/her data.
Your application is set as "Private" access
When a participant has been deleted, they no longer are able to access your application's content with their existing account. They will also not be able to retrieve their deleted profile.
However they will be able to re-create an account (new password) in order to gain access to the apps contents.
Your application is "Restricted users"
By deleting a participant, the participant will no longer be able to gain access the content of your application and they will not be able to retrieve their deleted profile.
However, if you decide to create a new access for them on your application, you have to add him to your list of participants and they have to re-create an account (new password) in order to gain access to the apps contents.