I disagree with this assessment.
If Ukraine can continue of constant warfare within it’s 2014 boundary, Russia will have to continued to deploy troops and treasure to maintain their “gains”. Those gains will not be productive economically and will be a drain on the already fragile Russian economy.
Ukraine only has to harass, Russia has to control.
Russia is already starting to default on it’s obligations. Its economic collapse will take about 6 months. Ukraine just needs to hold out. Once the collapse takes place, Russia will be internally forced to withdraw troops.
Russia’s “default” is only happening because the mechanisms for them to pay in dollars were taken away from them because of the sanctions, and the bond holders refuse to allow payment in rubles as an alternative.
If you have money that no one is willing to take, why should you care if they then declare you to be in default?
You are delusional. If the Ukrainians keep it up Moscow may decide to flatten Kiev like it did Mariupol. Russia has the capability and the will to manufacture enough missiles with hyperbaric warheads to flatten Kiev at will and they won't shed a tear doing so.