Europe seems depending on natural gas from Russia - but Russia also seems dependent on Europe - so as far as sanctions, not sure who would blink first.
I'm not sure if Ukrainians should be happy to either be part of EU nor Russia. Cyprus is part of the European Union, but.. we all know how that went. Anyway, as for trade between Russia and Europe.
The European Union and Russia have a strong trade relationship. EU imports from Russia are dominated by raw materials, in particular, oil (crude and refined) and gas. For these products, as well as for other important raw materials, Russia has committed in the WTO to freeze or reduce its export duties.
The EU is the most important investor in Russia. It is estimated that up to 75% of Foreign Direct Investment stocks in Russia come from EU Member States (including Cyprus).
Source:
http://ec.europa.eu/trade/policy/countries-and-regions/countries/russia/