How to keep the Vatican City independent

Emperor/ King Napoleon was in the 19th century the first who said the Pope has to be independent. The Church needs to be separate from the Italian State. Then the Pope became the ruler of the Vatican City which is an independent City state. I have a story/ Worldbuilding where I'd like to know whether what I've done is realistic and makes sense or not. In this story, the Emperor is dead and the bourgeoisie of southern Italy don't want a monarchy any longer. They want to create a Republic. But the monarchy in the north of Italy is on the edge of collapse. The nobility in the north are scared that if they lose their last chance to keep the monarchy, the Church will decide that it's simply easier to give the Papal States to the Italian Republic and therefore the Vatican City will be abolished. <br><br>The Pope was ready to give up the Papal States. But the nobility threatened to cut any ties with the Church. They don't want to become normal citizens of a Republic with a new government. They want to stay as they are. In the end, the Pope decided to not give up the Papal States. Then the War against the Italian Republic began. But the north had also to fight against Austria because the Austrians wanted to keep their territory in northern Italy as well. The Austrians had a huge win in a battle close to the capital of the Papal States and the Pope fled to Rome. <br><br>Then some parts of the Papal States had to be given to the Italian Republic, but the Pope keeps the Vatican City and Rome where he is hiding and a corridor which connects these two cities. The Austrians then formed a new Kingdom which includes the rest of the former Papal States. <br><br>But the Vatican City is still independent. They are not part of the Church in the Kingdom. The Church is still connected to the Vatican, but the Vatican is not in charge of the Church anymore. <br><br>I'm simply not sure how realistic this scenario is.