If occupied DNR declares independence and Russia supports it...
Moreover, oil and gas are the only major Russian products which have been the need and demand in Europe. In a few years they are not here anymore, and I doubt anyone will miss Putin or self-Russia either. Quite likely the Russia under this leadership the national economy will drop in economic size and importance (GDP) estimates are to a medium-sized developing country level.
You are fairly good at propaganda. Let me start with that you cannot predict the future as you have no means or expertise to do it.
The alternative sources of energy are already being developed. However petroleum is far more than energy. Petroleum is the feed-stock to a variety of chemical industries. The importance of petroleum and gas does not diminish due to lower use in energy production.
Russia will survive even if there is no trade between Russia and EU. Russia can develop its own agriculture which is not difficult as it has the land and the population is small. The technology is already available.
Russia cannot have any shortage of consumer goods as Asia produces plenty. There is no fear of going back to USSR times.
The military equipment can be produced through joint ventures between other countries. For example Brahmos cruise missile seeker and software is developed by India. Russia does benefit from this collaboration as the resulting product improves its own capability.
Russia will do far better than your expectations. Russia does not need EU at all.
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after being polite in Crimea 
