Russia would be very happy to install a puppet regime in Ukraine, as long as they had some certainty this regime would be stable and subservient to their interests. We know for a fact that they don't care about necessarily invading other countries as long as those countries are subservient: they are not planning to annex Belarus, nor did they have any real problems with Ukraine as long as it was led by their preferred leaders and it was not making any overtures to NATO or the EU.

The exact same thing will happen in Venezuela: the USA will be happy with any leader that they have confidence will represent US interests, stop doing any business with Russia or Iran, and that they think will last. If instead another member of Maduro's party looks likely to win power, either now or in the near future, they will certainly not allow that to happen, even if it were to happen as a result of free elections.