Evangelization of Slavic tribes was very slow process. In Croatia it lasted for three centuries. First the elite then others. There were three directions of that process: Frank Empire, missionaries from Italy and Byzantine empire. It is naive to think that that was something apocaliptic. It was a very slow process, without sword and fire. Lots of our ancient believes is preserved in our todays believes. Most of the christian temples are build on the sites of old ones.
I must confess that i never heard that Tzar Dushan ruined the last temple. Even that is a true fact it doesn`t mean that old slavic believes were preserved in 14. century Serbia. Both of our countries were in position of very close and strong christians centres so it is hard to believe that old slavic believes could be so long preserved.
I`m very strong supporter of rodnovery or our native religion. During my study in university i dedicated a lot of time for old slavic believes. Christiandom started as a sect and today is the most powerful religion. I m very found with the idea that Slavs return to they old believs. If we look today we are all physicaly Slavic but spiritual Semitic :)