what is the demographic balance between Russian speaking, Russian orthodox and the rest

I tried to indicate that there is no such clear distinction. Whether you use religion or language, both the Western Ukrainian nationalists and the Eastern Russians are a minority, while the centre around Kiev (which is much bigger than the Crimea) is Orthodox and mostly bilingual, and its vote can change between parties. In other words, the key to majority is winning majority in the centre, and losing Crimea would not change that.

I'm not sure that the shifting alliances of the past necessarily invalidates my thesis that Russia will gain Crimea at the cost of its dominant influence in rump Ukraine..

You are assuming that the situation today or tomorrow will stay permanent. But there are several possible scenarios, and IMHO two of the most likely ones are:

• the Maidan revolution parties might lose popularity due to economic reform and the rush to NATO and then a new force on the ashes of the Party of the Regions could take over in the next elections; or
  
• most ethnic Russians in the East come to resent Russia's grab of the Crimea and decide to stick it out as part of Ukraine now but change their views after seeing how the new government fails to rein in nationalists, leading to a federal semi-break-up or a real break-up in a civil war before the next elections.

In short, I don't see how the loss of Crimea could lead to a significant permanent shift in the power balance.

_{*Lunatic*, n.
One whose delusions are out of fashion.}