1. The war between Russia and the Ukraine is going to end soon. (over time the EU is going to forget about this)
2. The EU will start to invest more into renewable energy alternatives. (Reducing their need to rely on Russian oil)
3. The Russians will find other countries to buy their oil. (Example : India and more African countries)
So in conclusion.... Russia will still sell the same amount of oil to other countries and the EU will still buy from them after the war, because their alternative solutions will take time to replace their need for oil.
The number 3 on your list is already happening. That was what Russia is doing during the time the sanctions are applied and maybe those countries who got the oil can resell it again to other countries for an extra price.