If Hitler was assassinated would the Russians have taken over

No, because then Germany would have many other http://military.answers.comilitary officials ready to take Hitler's place.

This depends on many factors, including when the assassination of Hitler takes place. If the assassination takes place before Hitler was able to unify the country, the country may not politically have been able to agree on a way to mobilize the country, nor join with Austria. Without a strong Germany, Russia would have been far less hesitant in assimilating adjoining countries such as Poland.