Have they ever been seperated before? (At the groomers, boarding at a kennel, on walks, etc.) If they were, how did they act? I know some dogs who have been together a long time who don't care if the other dog is gone, and then I know others that throw a HUGE fit when their "house mate" is out of their sight for even a second.

So, before you make the final decision, perhaps you could try to keep them seperated for a day or two and see how they act.