If the US "quits" Nato (they won't), then Nato is done.
Specifically Article 13:

After the Treaty has been in force for twenty years, any Party may cease to be a Party one year after its notice of denunciation has been given to the Government of the United States of America, which will inform the Governments of the other Parties of the deposit of each notice of denunciation.

Even if Trump becomes president, he isn't going to withdraw from Nato, he both can't* unilaterally, and also doesn't actually want to. So I'm not really sure what the point of this article is except fear mongering for the benefit of the European MIC.

*National Defense Authorization Act for Fiscal Year 2024 forbids the president from unilaterally withdrawing from nato. Now that may be unconstitutional (and I would say that act is unconstitutional, but lol that has never mattered for the Military.)