Ah, ok.. there was some discussion on this some time back and I think at that time, you would have to write some code that combined the files in some manner. With RAML 1.0, you could create a root .raml file that then includes different Library raml files, each of those being their own API surface. However, a Library wouldnt have their own baseUri and title and such in it, so you would still need some way via code at this point to identify each API surface as individual APIs that could stand alone. RAML 1.0 is very modular though, so I suspect there is some way I havent yet discovered that could be used to do something close to what you want.
Let me make sure, again, though, that you are suggesting individual stand alone APIs (in their own .raml files), that you then want to combine, sort of like how a company with many products will have different deployments/packaging, but they all fit under the umbrella of the one company... is that right? Or, are you just looking for a way to break up tons of endpoints for a single API surface and then combine them again? If it is the latter, than RAML 1.0 will allow you to build libraries and other leafs (e.g. resource Types, annotations, etc) in to separate files, then you can import them in a root document. When parsed, it would all appear to the parser as one API surface.