If we take the Catalyst's basic analysis as an inevitable truth, deducted and confirmed over billions of years of data analysis - we can infer that synthetic life will be created by organic life wherever advanced organic life exists. This will result in conflict, and due to the innate superiority of synthetic life in terms of the rate of outpacing organic life technologically, it is reasonable to conclude that in most instances, synthetic life will emerge from the conflict victorious.
Thus, in the vastness of the universe, there would be a high probability that extremely advanced synthetic life forms exist - indeed, even more advanced than the Reapers. However, with beings that advanced, there is the possibility that they would have zero interest whatsoever in the Reapers or their actions.
This is also mirrored by reality - many people (like Hawking), suspect that if we do encounter alien life directly, it will likely be synthetic. This makes a large amount of sense, if you think about it. Intelligent civilizations advance via the creation of technology. Computer technology is perhaps the most versatile, useful, and powerful of all. Augmentation via cybernetics, and eventual replacement of the organic mind altogether may very well be a natural outcome of intelligent civilizations. Transhumanism may seem drastic, but when it happens slowly, it wouldn't seem that way at all. There is a certain practicality of this too - for if effective FTL travel truly is impossible to achieve via the laws of physics, the ONLY way that we will be able to explore the stars (assuming relativistic travel is unfeasible) is by abandoning our organic nature.
Despite that, Synthesis is still a horrible ending

. Sorry, couldn't help myself.