Why do you think that? I don't see Russia taking over Ukraine. I see them fighting until Putin dies. But Russia won't take be successful in their stated goals.
Or the Russian army could collapse. This goes up if Putin dies. Please read some Eastern Front WW1 history to see how fast that can happen.
Now back to Guyana.
Full scale attack- They could not hold off Venezuela, except there is one caveat. Maduro cannot send his entire military on the attack. He needs them at home and to watch Colombia. So say he sends 20%. That is between 20,000 and 30,000 ground troops. Guyana can mobilize between 4-5K. What is needed now is a training program and the supply of light weapons. These do not have to be US or UK. They could be Brazilian, Argentine, or even South Korean. Establish the capacity for Guyana to conduct an insurgency and delaying actions.
Hybrid- Venezuela with external help (Cuba, Russia (mercenaries) undermine the government of Guyana. Start hitting the mining and O/G sector with sabotage. Spread out the small military and make them paranoid.
There has been a push within the OAS to have sanctions reduced. If Maduro attacks this is off the table. This is what I think it is about. Maybe he asks for a "cut" of the profits from the O/G finds claiming that it is territory Venezuela claims. And he needs the hard currency.