I certainly don't see any new Persian dynasty adopting Christianity. At this point Zoroastrianism is too deeply tied into the Sassanid state, and a new dynasty would be taking over the Sassanid administrative structure and inheriting the nobility and administrative class, rather than replacing them as the Caliphate did. I seriously doubt that a Christian Shahanshah would be considered legitimate by most of the Persian nobility, and therefore wouldn't last long. Even if this king refused to convert, at least one of his relatives almost certainly would to gain the throne. A Turkic conquest dynasty would probably try to take over the administrative structure in much the same way, and would assimilate fairly quickly much as various conquest dynasties did in China. They would need at least the tacit acceptance of the Zoroastrian clergy to govern Persia, if not outright support. Or, they would need to replace the government structure like the Caliphate did, which is a pretty radical thing to do, and one few conquerors in history have done. Hell, even Alexander just replaced a few people in the Achaemenid system and moved the capital to Babylon. So, a new dynasty might move the capital away from Seleukeia-Ktestiphon, but absent an ideological imperative I don't see much change in the actual governance of the empire.