If Mr. Chase had written things the other way (Carmela and Furio have a wild fling and she runs off with him) Would she really be happy? Would Furio be happy?

I say a resounding No! It would have never worked, and I am sorta of sad they took a great Character like Furio, and made him very 'out of character' on Season 4.

Carmela is used to a materialistic lifestyle and the salary of a "Boss" we have seen this time and time again in the show. Whenever she is upset, she tells Tony that money (or something materialistic) will placate her. (Money to donate to Meadows school, a Spec house, Real Estate, etc). Carmela is also very much hypocritical of Tony's chosen occupation, often feining ignorance, while she knows better. She is also very much the "keeping up with the Joneses type" (or in her case, Keeping up with Cusamano's).

All of these things are the very antithesis of what Furio Giunta portrayed. He was a modest man, from a modest area outside of Avellino Italy. He had an intense and dedicated loyalty to his Camorrista Clan famiglia, and was hoping to find the right woman to start his own family with. Furio's idea of relaxation is cooking or gardening, he is a multitasker who very easily separates his business from his non-business lifestyle. (A type B personality) he is happy to be a loyal soldier or maybe a minor capo but has no aspirations for higher up. He is content where he is at.

Furio would never be able to keep Carmela in the lifestyle she is accustomed to here in the US, and I don't see Carmela as being excited about making homemade wine or canning pesto and marinara.

And while Carmela would be enthralled with the countryside of Italy, and the crowded dirty streets of Napoli, I think she would quickly grow tired of the differences between Europe and the US. (Lack of convenience, lack of understanding the language and customs, lack of the materialistic type wealth found in the US.) She would quickly grow bored with it, and Furio.

They were never meant to be, and in all honesty, they never could be. Tony and Carmela are the perfect match for one another. And as for Furio? Perhaps he will find a nice woman who can appreciate him for who he is, and enjoy the more simple country pleasures in life with him.
He certainly deserves it.

Furio was one of my favorite characters on the show. Why? Because through him we were given a glimpse of how the criminal organization known as the 'Camorra' ran in Naples Italy, and we were shown the vast differences between Organized Crime here in the US and 'The other side'.

While of course, Mr. Chase is writing a TV series based on his views and story lines he wishes, there are a few things he did get very accurately regarding the differences of OC overseas vs. the US. Many people think that all OC in Italy is called "The Mafia" or "La Cosa Nostra" it isn't. LCN or Mafia, is specifically a term for the criminal groups known in Sicily. The Camorra is based in the Napoli region, the NDrangheta in the Calabrian provinces, Sacra Corona Unita and literally a dozen more.

Each of these organizations runs very differently than the other, however some do work in concert with one another. Territories between organizations are fiercy guarded, and clan and blood ties are much more closely followed. They are also much more violent (often targeting women and children) and more powerful than their US counterparts (as far as modern day Italian OC in the US. After 1990).

Organized Crime in the US is much more 'homogenized' due to the simple reason of immigration from the late 1800's and early 1900's. A vast mixture of Southern Italians emmigrated to the US, and blood/clan ties were lost. (Reference Salvatore Lucania -"Lucky Luciano" for more information on the beginnings of the modern US 'Mafia')

By having Furio Giunta come onto the scene, we were given a rare glimpse of what the Naples Camorra is really like. What there outlook is, how they operate.
The largest example perhaps being Annalisa Vittorio running the Vittorio family in her husbands place (Mauro Zucca, who was in prison for life). "In the US you would never see such a thing!" says Tony Soprano, and he is right.

Through Furio (who was given much life by the talented Naples born Federico Castelluccio)we see that Southern Italians and Northern Italians are still very much in animosity with one another (Almost in the same vein as the US Northerners calling the US Southerners derogatory names) much the same goes on in Italy. The Northerners feel the Southern Italians are little more than "Uncouth, criminal, and superstitious farmers."
(Remember Furio's rant about Christopher Columbus?)

The "code" each Italian organization follows can be much more strict, and the hierarchy much more stratified than what is currently run in the US. "Omerta" the code of silence is followed much more strictly by the Italian OC, where as here in the US, everyone is "flipping states witness" or writing a book about their Mafia experience. (Reference Sammy "The Bull" Gravano)

Through Furio we were given a true glimpse into how these very old men of honor operate and the traditions they follow. One of the Italian soldiers called Paulie a "Classless piece of shit" and in the Italian's eyes, they have little regard for the US run OC or "Mafia". There is very little honor, tradition or 'silence and discretion' in the US they feel. Whereas Tony Soprano is often shown as a "sociopath" we see Furio is able to separate "Business" from feelings and is very much a renaissance man. Truly enjoying socializing with those he cares about and enjoying the feeling of large extended family. In Tony we see almost the opposite.
In Furio we see someone who is actually very levelheaded and is very dedicated to upholding his "oath to his famiglia and blood ties".

While I felt the whole Carmela-Furio storyline in season 4 a bit over the top and 'soap opera-ish' even then, he stuck to his codes and values. (Thus leaving the states).*

We see in Furio a man who is not truly happy hear and becomes rather 'disallusioned' with the US's version of the Mafia. I think this most of all would be something that would bother his heart, and Mr. Castelluccio portrayed this wonderfully.

So perhaps my greatest love of Furio is that he was able to give us a glimpse into something we don't really see anymore here in the US (thanks to the crackdown by FBI and other law enforcement agencies) and that is the way the "true" mafioso heart is, the codes the follow and the way they operate. At least in Italy and in the Camorra.

* (and yes, I realize the real reason Furio left the show was because Mr. Castelluccio and D.Chase had a disagreement, I was speaking of the character)