What you can do is add a global variable in your [Code] section

[Code]

var
ApplicationWasUninstalled: Integer;

After that, in the InitializeUninstallProgressForm procedure you can set the global variable to 1 (Note: this function gets executed only if the user clicks Yes when they are prompted if they want to uninstall your application

procedure InitializeUninstallProgressForm();
begin
ApplicationWasUninstalled :=1;
end;

Moving on, you will check the value of ApplicationWasUninstalled in DeinitializeUninstall function

procedure DeinitializeUninstall();
begin
if ApplicationWasUninstalled =1 Then Begin
//your code here
end;
end;