The relevant US statute is The Computer Fraud and Abuse Act of 1986 (CFAA), which has been codified at 18 U.S. Code § 1030
Section 1030 prohibits unauthorized access to a "protected computer" under any of several conditions, and also prohibits unauthorized obtaining of information from a "protected computer".
Section 1030 (e)(2) defines "protected computer" The relevant part, (e)(2)(B) defines this as meaning a computer
(e) (2) (B) which is used in or affecting interstate or foreign commerce or communication, including a computer located outside the United States that is used in a manner that affects interstate or foreign commerce or communication of the United States
That would surely include the computers whch host Stack Exchange.
The offenses relevant to this question would be subsectons (a)(5)(A), (a)(5)(B), and (a)(5)(C) which make it a crime for anyone to:
[(a)(5)(A)] knowingly causes the transmission of a program, information, code, or command, and as a result of such conduct, intentionally causes damage without authorization, to a protected computer;
[(a)(5)(B)] intentionally accesses a protected computer without authorization, and as a result of such conduct, recklessly causes damage;
[(a)(5)(C)] intentionally accesses a protected computer without authorization, and as a result of such conduct, causes damage and loss.
At least one of these subsections would apply to any of the scenarios suggested in the question, or any similar scenario. In all such cases the person or persons would be acting without authorization, or in excess of any authorization such persons had (as no one has authorization to destroy the site), and such actions would cause damage and loss.
Subsection (c) provides the relevant penalties:
(c) The punishment for an offense under subsection (a) or (b) of this section is—
...
(3)(A) a fine under this title or imprisonment for not more than five years, or both, in the case of an offense under subsection (a)(4) or (a)(7) of this section which does not occur after a conviction for another offense under this section, or an attempt to commit an offense punishable under this subparagraph; and
(3)(B) a fine under this title or imprisonment for not more than ten years, or both, in the case of an offense under subsection (a)(4), or (a)(7) of this section which occurs after a conviction for another offense under this section, or an attempt to commit an offense punishable under this subparagraph;
So such conduct would be punishable by imprisonment for up to 5 years, or up to 10 years for a repeat offender, as well as by a fine.
State laws might impose additional criminal liability.
In addition to criminal prosecution, section 1030 provides a right of private action under subsection (g) which provides:
(g) Any person who suffers damage or loss by reason of a violation of this section may maintain a civil action against the violator to obtain compensatory damages and injunctive relief or other equitable relief. A civil action for a violation of this section may be brought only if the conduct involves 1 of the factors set forth in subclauses [5] (I), (II), (III), (IV), or (V) of subsection (c)(4)(A)(i). Damages for a violation involving only conduct described in subsection (c)(4)(A)(i)(I) are limited to economic damages. No action may be brought under this subsection unless such action is begun within 2 years of the date of the act complained of or the date of the discovery of the damage. No action may be brought under this subsection for the negligent design or manufacture of computer hardware, computer software, or firmware.
Note that nothing in 18 USC § 1030 depends upon any "Terms of Service" document. The code section does depend on "authorization". Subsection (e)(6) provides that:
(6) the term “exceeds authorized access” means to access a computer with authorization and to use such access to obtain or alter information in the computer that the accesser is not entitled so to obtain or alter;
Subsection (e)(8) defines "damage", and (e)(11) defines "loss":
(8) the term “damage” means any impairment to the integrity or availability of data, a program, a system, or information;
...
(11) the term “loss” means any reasonable cost to any victim, including the cost of responding to an offense, conducting a damage assessment, and restoring the data, program, system, or information to its condition prior to the offense, and any revenue lost, cost incurred, or other consequential damages incurred because of interruption of service;
In addition, although I know nothing specific about the internal design of Stack Exchange, I would be astounded to learn that it does not include a robust backup system, so the idea that a rogue moderator or hacker could "destroy the site" so that it could not be put fully back online in a fairly short period of time is impluasible at best.
I suspect that the SE servers also include code that will detect and stop or pause widespread unauthorized deletion, but that is just a guess.
In an case, neither backups nor internal protections depend on any provision in any TOS document. Nor do the various criminal statutes.
