From the 1985 to 2019, I understand that SOX lighting was the only form of low pressure sodium lighting for general lighting applications because SLI/H lamps were discontinued in 1985 and other types of general lighting low pressure sodium lamps such as the SO/H, SOI/H, and NA-9 have already been discontinued before then. Astronomers tend to prefer low pressure sodium lighting near their observatories since the monochromatic wavelengths from these lamps can easily be filtered out in order to view the heavens very clearly. Unfortunately, since SOX lamps have been discontinued, there are hardly any real alternatives to low pressure sodium lighting for these applications. As a result, will astronomical observatories be forced to shut down as a result of increasing light pollution from LED retrofits?

They dont need exactly the LPS, any light with few wellknown distinct lines is good for this purpose.
In fact clear MVs were OK before LPS,...
So it could be some specific LED wavelengths will be OK too. The fact is, there is no high efficacy light source for that use beside the SOX, but on the other hand we are talking about very few places, where the higher energy consumption could well be justified.
On the other hand LEDs allow better beam control, so general reduction of the skyglow could be expected. And that is good thing not only for astronomers.

Tiberias and lots of settlements in Israel, have much brighter skyglow, once they replaced their HID streetlighting to LED. See here:

The problem is that LED doesn't have any beam control for make it cheaper, they are brighter than the original streetlights and irradiate in pretty much all the spectrum with wide peaks at blue and yellow wavelengths. With all that the observatory will significantly decrease its effectiveness and could become useless for some things. It could still be able to look object millions of light years away but it can't look for the object composition by the spectrum due to the high spectrum pollution, and it could easily give false results. Developing a filter to counter the LED spectrum would be expensive if not impossible, because of the wide spectrum there will always be a wavelength that could not be cancelled by any element.

It is like firing up an old spark radio that emmitt in all the spectrum near an airplane control, all their system will fail.

1) The US has virtually no LPS lighting.
2) The US has an incredible number of observatories.
3) Therefore, astronomy is not heavily dependent on the use of LPS lighting.

There's no problem for observatories to use LPS, MV, MH or HPS, because are well known wavelengths that can be counted by applying a similar chemistry to the filter. The problem comes when you use wide peaked spectrums, which can't get countered properly and there always will be pollution leaking through.

1) The US has virtually no LPS lighting.
2) The US has an incredible number of observatories.
3) Therefore, astronomy is not heavily dependent on the use of LPS lighting.

Alaska had LPS streetlights because there are several important observatories. They replaced them with lime green LED streetlights.

There are some observatories in the Atacama desert, because the sky is very clear there and it's far enough from the cities, but nearby cities went LED, which isn't smart. SOX would be the best, but it never became a thing here, so the cities were HPS.

Alaska had LPS streetlights because there are several important observatories. They replaced them with lime green LED streetlights.

I understand this isn't your native tongue, but your statement has nothing to do with mine, so why the quote? it's like you didn't even read what I said.

1) The US has virtually no LPS lighting.
2) The US has an incredible number of observatories.
3) Therefore, astronomy is not heavily dependent on the use of LPS lighting.

The same goes for lots of Europe. The number of observatories may not exactly be incredible here, but I never heard them complaining that they have to close because no one around uses monochromatic light.

From the 1985 to 2019, I understand that SOX lighting was the only form of low pressure sodium lighting for general lighting applications because SLI/H lamps were discontinued in 1985 and other types of general lighting low pressure sodium lamps such as the SO/H, SOI/H, and NA-9 have already been discontinued before then. Astronomers tend to prefer low pressure sodium lighting near their observatories since the monochromatic wavelengths from these lamps can easily be filtered out in order to view the heavens very clearly. Unfortunately, since SOX lamps have been discontinued, there are hardly any real alternatives to low pressure sodium lighting for these applications. As a result, will astronomical observatories be forced to shut down as a result of increasing light pollution from LED retrofits?

No

https://arstechnica.com/science/2019/10/how-flagstaff-arizona-switched-to-leds-without-giving-astronomers-a-headache/

Flagstaff, Arizona (where the Dark Skies movement likely originated due to the city's proximity to Lowell Observatory) has been looking at some solutions since Philips announced the discontinuation of LPS a few years ago. One involved yellow filters on otherwise "white" LED fixtures (a technique employed on the Big Island in Hawaii) but one would end up with a yellowish-green light (background in picture on article)

The other was "Phosphor Converted" LEDs (same principal with White LEDs but the phosphor mix is modified to produce a more yellow or orange light vs a pure white color. I know of one installation in Temecula (located near Palomar Observatory) using such lights. The color is somewhat similar to HPS

Then there are narrow-band LEDs that only produce light of a certain wavelength. I've read about such lights being utilized in some areas to avoid impacting nocturnal wildlife (particularly sea turtles). In that case, the wavelength was required to be 580nm or higher. A couple places I've read about used LED fixtures with wavelengths that peak at 620nm which would be red although I've also found products with 590nm which should be close to that of a LPS lamp.

Alaska had LPS streetlights because there are several important observatories. They replaced them with lime green LED streetlights.

Oops! Its Hawaii not Alaska like I thought before.

I do recall an article on TV some years back where an astronomical fraternity were complaining that they had to keep moving further and further away from Birmingham due to the spread of HPS lighting replacing SOX installations. This would have been in the 1990s I believe.