I don't believe a world war will result from Putin's actions in Ukraine but his stubborn need to reclaim that country could result in a messy internal struggle for power and rights and land.
Russia is economically poor at this moment - despite billionaires springing up all over the place - and Putin is desperate for some positive political news to keep everyone at home quiet. He's not a dictator in the extreme but it's worrying that the right wing extremists are growing in confidence. Media oppression is common and gays and other outspoken groups are being targeted. Bad news for social justice.
It's said that with Putin you have to show strength against him to gain his respect but there's not much the west can do - sanctions won't help - diplomacy might help in the long run but won't stop Russia provoking Ukraine in the short term - and massing western troops is just going to poke the bear and annoy him.
This situation will rumble on and on until the businessmen in Russia start to ask questions about Putin's value as leader and he's forced to act - by removing some of his troops to increase business confidence.
OR the situation might escalate if there are deaths for either side, then there'll be fighting- small arms and artillery perhaps? - followed by TALKS held via the UN.
I hope both sides can restrain themselves. Ukraine and Russia have so much history between them but also a shared culture and many family ties.
The question of Crimea will remain. The answer? Perhaps Putin has answered that already. It's a part of Russia. As long as he's in power.