They had a whole year to do whatever they wanted prior to Maduro being snatched. For starters, they could've provided mercenaries and bodyguards that would've made this whole raid impossible.Maduro fell in like three hours. wtf were they supposed to do? Putin and Xi Jinping barely had enough time to just get briefed about the bombing and then boom the dude is under arrest on a US warship. if he had survived for few days then maybe Russia would have done something though even that is quite difficult due to distance.
But the better question isn't what they were "supposed" to do, it's why should they sink resources into an irrelevant country? If USA tries to invade and occupy Venezuela, it'll either become a nightmare like Afghanistan's occupation, or it'll fold and accept the new regime very quickly.
Either way, whatever aid and preparation Russia/China provide will make very little difference because this is the sort of things that either goes very wrong or very right. So really, there was no point. Maduro should've been better prepared.