Provided that there is nothing for the photon to interact with (i.e. we look at it in vacuum), the mean free path will be infinite; that is, it will continue travelling forever in a given direction. There's nothing which will stop the photon's path. Hence, it will go arbitrarily far. Whether you have a single photon or a laser, the answer won't change.
The fact that photon lines will never end manifests itself in another relevant fact. If you look at the intensity $I$ of light on a sphere of radius $r$ away from a point source, the intensity drops off as $1/r^2$. More specifically, if $P$ is the power of that source, then $I(r) = \frac{P}{4 \pi r^2}.$ The $4 \pi r^2$ in the denominator is just the surface area of the sphere.
You may think this is relatively trivial, but in fact, it's actually a pretty deep fact. We know from 20th century work that there are particles similar to photons but with some differences. One of these is the $Z$-boson. 580
Unlike the massless photon, the $Z$ boson is massive. Its mass is around $91 GeV/c^2$, which is about 97 times as massive as a proton. If you did the corresponding analysis for $Z$-bosons, you'd find that they decay, and the decay length is on the order of $10^{-18}m$. A $Z$ boson will on average only travel about that far in vacuum. This leads to a different functional form for the above intensity, which will have an exponential dampening. In fact, this mass is essentially equivalent to studying photons in a medium which provides dissipation (e.g. inside a superconductor).
The fact that the photon doesn't suffer this same fate is really a consequence of its masslessness. There are many possible bounds on the photon mass. Of course, just the fact that we see photons from very long distances away provides a (rather strong) upper bound on the photon mass, though it is perhaps a bit deceptive as there are certain unusual models which avoid this strong bound. The most robust, model-independent bounds we have to date are about $10^{-14} eV/c^2$, that is, a factor of about $10^{23}$ lower than the proton mass. 795