Dissolution of the EU? I don't think it will happen, if one or more members veto the decision, it will be postponed indefinitely. ( that's the way it goes, isn't it? )
Turkey has a lot of issues to deal with, how about the fact that it's essentially a military state thinly disguised by democratic procedures? Their human rights record is still not adequate, its economy will take years to reach the level of member states, and how about the Kurdish and Cyprus issues? Those have to be resolved as well.
If they manage to deal effectivelly with those things in say, 10-15 years from now, I think it's for the EU's best interest that they join.
What is the time span with regards to Turkey's admittance? Ten years from now, five years, perhaps a year?
As for December, I don't think that Greece is going to approve unless they get tangible assurances that the Cypriot issue will be resolved. And I also think that France and Germany have serious reasons to veto the decision as well.