If the star cannot be seen with the naked eye or a telescope, the light has diminished to where no telescope can magnify it.
The problem is your failure of scale, and in understanding the physics of light.
A particle of light is
not like a balloon deflating as distance increases to an object, slowly letting out energy until it's entirely depleted, and being sampled from some growing field, which is how you seem to be treating it.
Rather, it's like a shotgun blast, but the pellets never lose speed or momentum (ok, they do a little through red shift due to expansion, but not much at most reasonable scales).
The reason distant things are difficult to see is that in the arc width of the emission surface, there are only so many photos and there is a lot of dust in that mostly empty space that will catch much of it. It will be received by whatever receives it in a compressed emissions spectrum (pesky redshift...).
From the qualities of this light we can make inference about what is there: the emission spectra may match a compressed hydrogen spectra, so we know there is hydrogen; the spectra is so compressed so we know how far.
We don't need many photons, or frequent photons, to infer these facts. All we need is the occasional one or two! All we need is a few lucky survivors that miss all the obstacles.
We can see all the way to the quark-gluon plasma epoch of spacetime, albeit that epoch of a region very far away from us, with mere photons (we don't strictly know how big our gravity cone is...). The only places we cannot see in the universe are not due to light attenuation but due to space and matter at that time and place being *opaque* to all light, as a literal wall.
We can even infer how long the light has been traveling from the shift, and we use this (ok, a similar) principle commonly with laser ring gyroscopes, which are what keep a plane from losing track of its orientation. We literally can time how long the laser takes to travel the ring.