Are you listening to yourself my man?

I work on optical systems for the military, so I thought I'd weigh in with actual science, yet you've gone off on this tangent about how "I can't see it because I'm inside it." You're sounding rather hypocritical no?

But to address your point of an object not "winking out of sight"...if you're actually interested in learning...

Imagine looking into a body of water. If it's deep enough you won't be able to see the bottom. I assume you realize that you have refraction and sediments and particles ect ect. All true. It's also true that air is a fluid, just not one that's dense enough to hold sediments, yet it still holds things that cause light to deflect. It's not just refraction friend, but also reflection, absorption, scattering, and a few more things.

Both camera lenses and your eyes work by taking in light and they see the light that's reflected off of objects. Let's starting putting this all together aight? If the light bouncing off of an object is reflected, refracted, absorbed, scattered, and more by the time it reaches your lens, it will become more difficult to see. The more light emitted the more clear the image, hence the further the light of an object has to travel through a medium(air, glass, water, ect) the less likely you are to be able to make out what it is clearly...which is why the military goes with 'detect' and 'identify' when designing optical systems...but maybe that's too far off topic.

Thus, going back to address your heli example, no, it would not be visible forever in that scenario if the Earth is flat. Assuming the Earth is flat in your heli example, the heli would obviously get increasingly smaller as it departs, which obviously makes it more difficult to see. However, the amount of materials in the air that can interfere with light's travel would also increase, so you would also see the heli get fuzzier until it 'disappears'.

And if for some reason, none of that rings as true for you, perhaps you would consider this google maps link: https://www.google.com/maps/dir/28.190254,-80.5950473/28.4522586,-80.5566903/@28.3177039,-80.5401822,11.5z/data=!4m2!4m1!3e0?entry=ttu

From this beach you can see Canaveral's launch buildings on most days in most reasonable conditions. It's 16 miles away. According to ChatGPT, the calculation of the average person standing with their feet in the ocean should only be able to see roughly 2.88 miles before considering atmospheric conditions....but nah of course, reject the evidence of our eyes and all that 1984 shit