Thanks for the question.
If a person were to make their country an idol which they hold above God, and they do so knowingly and willingly, then yes, there is a good chance they would lose their salvation.
The First Commandment requires us to hold nothing above God so this could be a serious matter.
That being said, ordinary devotion to country and patriotism is not a sin, and does not compete with devotion to God, but is actually an extension of the Fourth Commandment: honor thy father and mother. The word nation derives from natus, or born from, and terms such as patriot are derived from patria, or father land. There is a familial connection to our country as we are born kin to one another, and thereby are an extended family, albeit not of blood or even faith at this junction. Still, we share a common heritage and it is something to cherish.
Whether someone has usurped the right order of true patriotism only God knows, so we cannot judge men's souls.