Learn Farsi: تا زمانی که پادشاه زنده است، این سلسله حکومت می‌کند. - As long as the king is alive, this dynasty rules.

While many conjunctions expressing conditions or time (like تا for 'until') trigger the subjunctive, تا زمانی که (as long as) emphasizes a parallel, ongoing factual duration. Because we are stating a current, ongoing fact ('the king is alive'), we use the indicative mood for both clauses to show that one fact guarantees the other.

Could the main clause use the future tense instead of the present indicative (حکومت می‌کند)?

Yes, you technically could say حکومت خواهد کرد (will rule), but Farsi generally prefers the present indicative for these types of factual statements. The simple present is highly idiomatic for expressing an ongoing, guaranteed result that is happening now and will continue.

Is there a difference between پادشاه and the simpler word شاه?

They both mean 'king' and are often interchangeable. However, پادشاه is slightly more formal, historic, and majestic. It pairs perfectly with grand historical concepts like سلسله (dynasty) found in this sentence.

Does سلسله strictly mean 'dynasty'?

Its root meaning is 'chain' or 'series'. In history, a chain of successive rulers forms a dynasty. You will also see this word used in everyday Farsi to mean a 'series' of events, or geographically for a mountain range (سلسله جبال).