Trump's 1st term ends at noon on January 20th regardless of how this shakes out. If a winner is not declared by then, neither Trump or Biden are sworn in. In that case, since there is no POTUS there as also no VP. It falls to the 3rd in line, Speaker of the House of Reps.
...unless the SCOTUS decided extend Trump's term. I don't think they would do that, and I don't think it would be constitutional if they did.
Cross the Rubicon is a very apropos analogy. Trump may have legal authority to suppress a conspiracy, but if the SCOTUS or the state legislatures don't overturn the election results, Trump has no legal standing to deploy the military and declare himself POTUS. The Constitution is very clear on how election results are to be disputed and resolved and nowhere does it mention military action. Unless the election is overturned in a way the Constitution proscribes, that action would be a military coup and Trump would not be President, but rather a self appointed dictator. He would have to rule by fiat since there is no way Congress would go along with that. The US becomes a banana republic. Furthermore I think it is highly unlikely any military leaders would obey such orders. They are sworn to defend and uphold the Constitution of the United States, not the POTUS.
Any computer system can be hacked. What is truly damning is Dominion voting systems don't have to be hacked. The ability to delete votes or change them from one candidate to another is a documented design feature spelled out in the user manual, according to Sidney Powell.
Military members are not duty-bound to follow illegal orders. In fact, they are expected, and sometimes legally required, to refuse to obey them. They take an oath to “support and defend” and to “bear true faith and allegiance” to the Constitution, not to the President. I'm not a constitutional scholar, but I believe the actions suggested by the original post would be unconstitutional.