The best way to resolve the situation in Crimea in the event the residents want to separate from the Ukraine would be for Russia to purchase the territory. Russia could then allow the Crimeans to decide what status they wanted such as becoming an independent state or joining the other ethnic Russians in the Russian Federation.
I was going to include this suggestion in a post dealing with the
situation in general but decided the proposal would be more likely
to be noticed if suggested in a separate post. I
believe the Treaty of Guadalupe Hidalgo
which ended the war between the United States and Mexico in 1848
suggests a resolution of the conflict over control of Crimea.
A dispute over whether an area (occupied by persons who identified
with the United States) which is now the State of Texas was
independent sparked a short war between the United States and
Mexico. The United States easily won the war but then agreed
to purchase another part of Mexico that was attracting settlers who
identified with the United States. The purchase eliminated the
potential for a future conflict between residents of that area and
the Mexican government
Crimea is something of value so it would be fair for The Ukraine to
receive compensation for its loss. The payment for Crimea
could be thought of as compensation for money the national
government of The Ukraine has spent on the region for such
expenditures as government buildings or infrastructure items like
roads. The payment would replace tax money that would no
longer be collected from Crimea.
Payment wouldn't need to take the form of money. Russia
has ample energy resources and The Ukraine already obtains energy
from Russia. Thus, natural gas or some other fuel might
be used as compensation. The Ukrainian government
has had a policy of trying to keep energy costs down for
its citizens. Russia might significantly reduce
what it charges for natural gas for the next 10 - 20 years with an
implication that the discount would be passed along to
individuals. Russia might also offer to compensate anyone
wishing to move from Crimea to the Ukraine or The Ukraine to Crimea.
Ukrainian officials need to recognize the potential costs of trying
to force Russian Crimeans to stay in a country where they don't feel
they belong can lead to civil conflict including terrorist
bombings. The conflicts between Catholics and Protestants in
Northern Ireland and the actions of the Basque separatists in
Spain demonstrate what can happen. If some Ukrainians
decided to start a Balkans style ethnic cleansing campaign, Russia
would feel compelled to invade.