Well, Bohemia is still on the map, and having visited it personally few days ago, I can vouch for its existence. It is simply more commonly known today as Czech Republic (or Czechia), with the term 'Bohemia' being a Latin exonym derived from the Celtic Boii people and initially rendered as Boiohaemum or Boiohaemia (Boii themselves are rendered as Beheimare in the mid-9th century document Descriptio civitatum et regionum ad septentrionalem plagam Danubii by an anonymous scribe known as 'Bavarian Geographer'). The English and German terms 'Bohemia' and 'Böhmen' respectively are still used to denote one of the constituent region of Czechia (essentially the entire western half of the country), with the others being Moravia and Czech Silesia.

Now, what do the bohemian lifestyle have in common with this Central European country? Well, apart from the fact that some people of Czech extraction were partial to that way of life, not much, really. It is another linguistic-historical misunderstanding, this time related to the medieval migrations of the Romani people. They have arrived from India to Europe through the Eastern Roman Empire somewhere around 11th century (they are mentioned by Anna Komnena) and moved to the Central part of the continent, including Bohemia and Hungary in 13th century, from where they migrated further west, reaching France in late 14th century. This gave the false assumption that the Romani and other Indian migrant people came from Bohemia, hence the demonym (the oldest use of the term 'Bohémien' is dated to 1467 while the term 'Gitain' has been first recorded in French in 1661, in the translation of the earlier Spanish text). It is worth noting that this is related chiefly to the Western Europe, as in Central and Eastern Europe Romani people were usually called by a modified name used in Eastern Roman Empire (atsiganoi), e.g. rom. Tsiganesti, pol. Cyganie, rus. Цыгане, ger. Zigeuner with several Slavic languages retaining related equivalent of the word 'boheme' (e.g. pol. cyganeria, rus. цыганщина). By the way, the term Bohemien is not the only result of the false attribution of the place of origin, as folk etymology of the Western terms Gypsy or Gitan derives them from "Egypt' (at least partially due to the history provided by the Indian migrants themselves who found it easier to refer to the area most people were familiar with due to its presence in the Scripture).

Although the term bohemè is first recorded in reference to non-conformist people were first recorded in mid-17th century, it gained popularity few decades later, and had to be popular enough in the mid-19th century as they were used by e.g. Honore de Balzac or Louis-Henri Murger in the titles of the Un prince de la bohème and Scènes de la vie de bohème respectively. As the terms like English 'Gypsy' or French 'Gitane' were closely associated with the actual Romani people and their distinct culture, the obsolete term Bohemian was resurrected, so to speak, to denote people who were by no means related to the Romani and followed a free-spirited lifestyle that eluded many contemporary social conventions, per analogiam to the romanticized, vibrant image of the migrant Romani, living carefree life far from the constraints of 'bourgeois mores' and most often than not mixed with a hefty dose of the imagination fueled by the burgeoning Orientalism. It goes without saying that the actual life of a highly visible migrants in the largely absolutist and war-torn 19th-century Europe was usually far from glamorous.

So, the term 'bohemian' referring to the non-conformist people, often of artistic persuasion is derived from an old name of the Romani people used in Western Europe due to false assumption they are in some way related to the inhabitants of what is now Czech Republic used to evoke the specific associations with the actual Romani.