I do believe that, usually, you should make it possible to be archived. (In one of a few cases where it isn't, consider if HTTP(S) is even the correct protocol for what you are doing; sometimes it isn't.)
I agree that you can (almost always) write HTML without JavaScript codes (CSS is not always needed either, but nevertheless it can be helpful). This improves portability too. If you do want to use JavaScript to generate static documents, consider using Node.js and have it output a plain HTML document, which will then be the hosted document, rather than hosting the JavaScript version. (This way, the code only has to run once.)
About fonts, I think usually the fonts are not an essential part of the document. (Still, you don't usually need to use so many, but often you do not need to specify the font at all, except you may still need to specify if it is monospace, bold, etc.) Also, you do not usually need so many pictures on your web page (except picture galleries).
I do think if you need a copy of a web page then you can copy it.
You can also use plain text documents (without HTML); it is what I often do.
"monospace" is a property of a given font but is not (usually) a variant of a single font family as is "bold" (font weight).
While bold text is often used for emphasis and setting it to "regular" doesn't change the meaning much, using a monospace font signals specific things (often, it's used to represent code snippets, but in some contexts it can mean "work in progress"). Changing that font to a proportional one strips a lot of meaning and readability from the text.
In that regard, fonts families are an essential part of the document, and not just their stylistic/emphasis variants (e.g. size and weight, which can still convey important meaning on their own. Think titles and headings.)
Even Glk, which has styles meant for meaning and use rather than formatting, nevertheless has a monospace style, since some things need to be displayed using a monospace font to be displayed correctly. However, you could just as well display all text using a monospace font, if you are using only one font, so you might not be able to "signal specific things" by the use of a monospace font.
For the case of headings, this can be done without specifying the font yourself; if you specify it is a heading, then the rendering software can decide how to display it. (HTML has <H1> and <H2> and so on for headings, and Glk has style_Header and style_Subheader.)
Honestly, in almost all places that monospaced fonts are used, they’re purely a stylistic choice. (The remainder is mostly ASCII art, or plain-text representations of tables—in which case alignment is important, not the font—or something where tabular figures are desirable for number alignment.) I don’t say that that makes it useless in any way, but honestly monospaced text in code editing is overrated. You can live without it easily, and will probably get used to it very quickly.
I agree about monospaced text in code editing. I was thinking about uses such as code excerpts in literature (class names, inline bash commands, etc). Monospaced fonts[1] plays a major role in helping reading and understanding the content. This is more than a stylistic choice.
[1] actually the font doesn't need to be monospaced, but it must be very different than the font used for main copy.
While in some cases the font doesn't necessary need to be monospaced, some documents might require that a monospaced font is used, so it should be monospaced anyways. Although, as you say, different from the main copy; so if all of the text is monospaced, there should be some way to distinguish it, such as by selecting a different monospaced font, or displaying it with a different colour.
(One case where a monospace font is required is if you are automatically including text from another document which uses plain text format; there is no way to determine what format is needed, but monospace will always work.)
Regarding fonts, I think it's good practice to archive fonts together with your site's source, if the site relies on third party resources, like Google Fonts. (Switching the link target should be easy. Embedding a commented link to a stylesheet linking to these local resources along with the third party resource link may be of help.)
I agree that you can (almost always) write HTML without JavaScript codes (CSS is not always needed either, but nevertheless it can be helpful). This improves portability too. If you do want to use JavaScript to generate static documents, consider using Node.js and have it output a plain HTML document, which will then be the hosted document, rather than hosting the JavaScript version. (This way, the code only has to run once.)
About fonts, I think usually the fonts are not an essential part of the document. (Still, you don't usually need to use so many, but often you do not need to specify the font at all, except you may still need to specify if it is monospace, bold, etc.) Also, you do not usually need so many pictures on your web page (except picture galleries).
I do think if you need a copy of a web page then you can copy it.
You can also use plain text documents (without HTML); it is what I often do.