What happens to my contents ?

Thanks for your question.

However, this plugin doesn’t allow Administrators to delete their own accounts since they already have the delete_users capability.

If you were NOT an Administrator, then deleting your account with this plugin would simply move your content into the Trash.

In the WordPress core, when an Administrator deletes an account, reassigning the content from that account is already an option given. So I suppose, just have another Administrator delete your account and reassign it’s content to someone else.