Upgrade or migrate/ Rejoin separate external library's

Aperture 2 has nit been supported on MacOS X and been having more and more siince version 10.7. You have been lucky, to able to use it all since then. If you want to continue to work with Aperture, upgrade. There will be a compatibility upgrade for Yosemite, so you can expect to be able to use it with the next version as well, at least for one and a half year. But it is really for you to decide, if you are willing to pay the 80$ after the announcement of the demise of Aperture.

I have not much experience with Lightroom, so I cannot give advise on how to migrate. Afaik, Lightroom cannot read Aperture libraries. You will need a working Aperture application to be able to export your images with all your edits and metadata tags, unless you are happy with migrating only the originals.

The successor to Aperture and iPhoto, "Photos.app", is supposed to be able to read Aperture libraries and to support the advanced features of Aperture. You may want to wait for the release of "Photos.app", to make your final decision about the migration.

Ouch. You have a bit of a problem.

If you search you'll find lots of tutorials for switching from Aperture 3 to LR. Basically the problem lies in getting information Aperture stores about your photos (keyworks and other metadata, organization like projects/albums, and edits to the photos themselves) into a form LR can use. It can use standard photo metadata easily. Organization is a bit tougher, but can be accomplished via keywording, folder organization, and some other tricks. Edits are basically stuck in Aperture; you have to export an image to preserve them in a new DAM (unless and until you can switch to Photos when that comes out). There's really no way to simply import an Aperture library into LR (or vice versa).

Most of the solutions rely on being able to use Aperture to export, or move masters, or whatever. Seems you can't do any of that. I also assume you are using non-referenced photos. I don't think merging your libraries will make the process of moving to Aperture 3, Photos, or LR any easier, but iPhoto Library Manager might be able to do that for you.

But there are still ways; it just depends on how much work you wanna do. Aperture libraries are just package folders; your masters are in there, just hidden. You can make use of aliases, or even changing the name of the Aperture library itself, in order for the Finder and/or LR to see inside that masters folder and find your photos. BE CAREFUL though; research what you're doing before you jump into that. I use LR to reference files that are within a current Aperture/iPhoto library but messing around in there can have some bad results with Aperture if you don't know what you're doing. But it can also save you if you have no other way to access those photos. You could also just manually copy them out of there, perhaps a safer route.