What happened to the original Silesians
What do you mean by real Silesians?"
The region was named by a Slavic tribe hat lived here in Early Middle Ages before any Polish or Czech national identity appeared (all Western Slavs consisting of a dozen or so tribes spoke more or less the same language and were spread from North Sea till Danube and Bug).
But of course they weren't first in Silesia...
Lets forget the megalithic "Stonehenge builders" - "original inhabitants of Europe" but after them came Celtic tribes (that left animal-like statues on the top of the holly mountain Sleza (which become also the religious centre of Slavic Silesians a thousand years later). Name Bohemia also derives from the name of the Celitc tribe. Then came some Germanic tribes which all left towards Roman Empire in Vth century living he land east from Elbe nearly uninhabited till the Slavs came from the east.
Till this time tribes were so unnumerous that they could just "pack and leave" as Germanc tribes did so the land changed it's inhabitants quite fast.
Then the times of Early Slavic kingdoms came and Silesia was incorporated into Polish territory but still being influenced by Czech. Then after the death of Władysław Krzywousty in 1138 the country was partitioned between his sons, and their land also between their children etc. which created a mass of small fighting duchies. These in Silesia came more and more under influence of Czech which was a powerful country during this period. At he same time German cultural influence increased. To have more power rulers needed more money, to have more money the needed more taxes, to gain more taxes the needed more people. The country during this time was a vast forest with some villages. A plenty of land to inhabit. So the rulers started colonising their land using people from region witch overpopulation which wanted to live for a better future. An those were colonists from western Germany that were given the land, cutting he forests and establishing villages and towns. They appeared in XIIIth and XIVth century throughout Central Europe (see for example Transilvanian Germans) but in Silesia hey were most numerous they brought their culture language etc. and soon they overpopulated the Slavic Silesians in the southern and western Silesia. And trough ages Slavic Silesians mixed with German colonists taking their language and culture. (the same happened in Pomerania or otherwise in the more eastern Poland - where German colonists were a minority that took up Polish langage and culture living only the names like Tymbark, Szymbark Gorlice etc. - in Kraków St. Mary's Cathedral last masses in German were given in XVIIIth century).
I can say that throughout those centuries the Silesians from western Silesia become 100% Germans.
Only in the easternmost Silesia at the border with Poland still some kind of mixture culture Survived which is known today as Silesian - but have probably very little in common with medieval Silesians - it is rather a result of German influence on Polish people that settled there since XVII th century (since that time Polish become again more "vital" than Germans and started moving west and north - see Masurians). Also some of the eastern parts Of Silesia were were under polish influence till XVIIth century (nearly whole Upper Silesia - some duchies under Polish control (Racibórz, Pszczyna) or properties of Krakow's bishops.