Setting aside the specific terms of service that might apply in this example, some basics on copyright law in the internet age might help.
The economic right is held by the author and may be assigned to another party or, in some jurisdictions (such as the US), dedicated to the public domain. Alternatively that economic right may be retained and the material licensed to another party as a bespoke license or more generally as a public license. The terms of that license are material: a license may be revoked by one or either side accordingly or implicitly withdrawn through nonāperformance such as the failure to comply with the obligations set out in the license (for instance, the need to retain the license notice on otherwise legitimate redistributions). In passing, IĀ am personally interested in public licenses that also class as open licenses, such as the Creative Commons CCāBYā4.0.
Alleged breaches of the license terms can be prosecuted under copyright law and also under contract law should the prevailing jurisdiction allow (for example, consideration is required under UK contract law and is necessarily lacking for material under public licensing). In some countries (such as France and Germany), a moral right may exist in addition to the economic right. In any case, it is useful to distinguish between the copyright owner specifically and the rights and obligations licensed to third parties or the public more generally.
One can view a license as ādeĀ facto ownershipā but that is not an especially accurate description. Better would be to note that the ability to force licensees to behave in a particular way is related to the jurisdiction, the terms of the license, and the actual actions, including omissions, of that licensee.
The identification of legal jurisdiction is especially problematic for material distributed via internet sites. Some licenses specify a choice of law but that may not necessarily apply or be enforceable. In which case, consideration of who has legal ownership, technical control, and legitimate access, together with the location of hardware, if identifiable, becomes material. Along with more general legal doctrines covering territorial scope.
There is no general right to have material deleted once legitimately published. That process depends entirely on the terms of the license granted when made public, the prevailing law, and the ability to locate and persuade or force publishers and other intermediaries and services to act in accordance with your wishes.
Indeed useful to think carefully before publishing material via the internet (this posting included) and to be aware of the difficulties in effecting deletion once made public.