When diplomatic solutions seem impossible parties revert to military measures to shake up the pieces.
When such shake-up produces a military stalemate then it is time to reconsider a diplomatic breakthrough.
On the Ukraine Eastern front a military stalemate is rendering the war sterile. Moscow will not let Kiev re-assert their sovereignty over the pro-Russian Eastern part of the country and will continue to use stealth in inducing sufficient resources to ensure perpetuity of the stalemate until Kiev is exhausted.
On the other Moscow cannot conduct a full scale invasion of Eastern Ukraine as that could trigger a full scale war with the West, which Moscow has no appetite for given its weak economic point of departure and the crippling economic sanctions that would follow.
So unless parties are willing to endure an endless war of attrition with the Western and Eastern parts of Ukraine acting as proxy version of a new cold war between Russia and NATO, the parties should immediately re-engage in a diplomatic effort to break the deadlock.
Before things become more serious, there needs to be a UN-sponsored international conference where a diplomatic solution is reached that represents a compromise between the two current extreme positions. The compromise has to take account these factors, even if they could seem prima facie contradictory. The following could be a framework for negotiating a diplomatic solution which takes into consideration all parties' interest in the conflict:
1. The safeguarding of Ukraine entire sovereign territory.
2. The recognition of Russia’s interest in Crimea through some sort of land lease agreement similar to Hong Kong’s status before its reversion to China in 1997.
3. The recognition of Russian interest in maintaining a NATO-free buffer zone between its borders and NATO countries.
4. The recognition of the rights of ethnic Russian majorities in Eastern Ukraine to a large degree of autonomous self-administration.
5. The recognition of the right of sovereign Ukraine to seek cooperation with and, if necessary, membership of the EU.
The Cold War was buried in Malta in 1989 through the Bush Gorbachev meeting. Malta could offer to host such a UN sponsored save Ukraine international conference.