For most other continents, yeah, it's not hard to maintain a realm with about the bare minimum of nobles. On Dwilight, it usually equates to a drawn out spiral into death. It might take a few months, maybe a few years, but what happens is that a player joins, sees that the realm isn't doing too well, or can't provide whatever it is the character is seeking, and leaves. The realm never makes any significant advancement, or if it does, it falls back down in short time.
Dwilight is indeed large, and a lot of its land is ready to be developed. But right now it looks like the desire for uniqueness is so great that realms would continue to try to be independent and risk being stuck at the sub 15 nobles mark for a long time, possibly until death. Just saying...If Aurvandil didn't secede and worked with Madina to actually populate that really good island location...Or if the Barcans actually contributed to D'Hara...
Obviously this wouldn't happen due to human differences. But alas, it is interesting, and provides some support to my one true "fear" of Dwilight. The victory of the wilderness over man.