The Cylons as a group are divided at the end of the series.
All copies of the friendly humanoid models (2/Leoben, 8/Sharon, and 6) settle Earth with the Colonials. They apparently die out without leaving any descendants, as Hera was the most recent common ancestor of all humans today. This group also includes the three surviving "Final Five" Cylons from Old Earth, though these are not the same group of Cylons.
3/D'Anna stays on Old Earth to die alone.
It's not expressly stated what happens to the unfriendly humanoid models (1/Cavil, 4/Doral, 5/Simon). Many are killed in the destruction of the Colony, but some may still be out there somewhere at the end of the series. But without a resurrection hub, and no ability to reproduce, the organic models will eventually die out. It's imaginable that they could find some way to reproduce, but it seems unlikely given their failure to do so during the series, compounded now by their lack of females.
The mechanical models subservient to the 1/4/5 group may survive indefinitely, but they all have some sort of behavior inhibitor built in, so it's difficult to say what they'll be able to do once the organics die out. Probably similar options to the friendly mechanical models.
The friendly mechanical models leave Earth in the basestar, to find their own destiny. No further details are given in any source, and we have very little context for guessing what they might decide to do on their own. Whatever they did, they did it in such a way that we see no evidence of them now. So we can reasonably say they never returned to our solar system in a fashion that left evidence. We can also reasonably say that they and their descendants never colonized the entire galaxy or built any visible megastructures in the few million years available to them.
These centurions were apparently interested in their own short-term survival, as they didn't commit suicide with the rest of the fleet. Any plan for long-term survival would require a resource base, so they would presumably need to find some resources somewhere. Their survival requirements are very different from humans; they could live in much harsher environments. They could literally colonize an asteroid in interstellar space without problems.
Besides "go found a peaceful civilization" they don't have many other touchstones to involve themselves in. One might suppose they would go try to free their enslaved brethren (or take revenge on any surviving 1/4/5 models), putting them back into conflict that could lead to their destruction. They could also explore the history of Kobol and the thirteen tribes, and find who-knows-what there that could send them off on even more interesting paths. And the angels might imaginably get involved and cause unimaginable divergences.
In short, we don't know, but it probably wasn't very interesting.