Events for a 4X space game, the player has up to 5 options how to respond to an event (choices). Like your scientist discovered the sun going nova, or you suspect that some planetary governor is stealing money, or a journalist is badmouthing your regime, etc.

Those events will be hand written (I'm not going to attempt any storyline generator algorithm). But what I want is to make them somehow parametrized and/or intelocked and/or chained. You know, so there is more replayability and more logic in what happens.

Ideas?

When I ran some tabletop rpg's I'd start by drawing a network of plots and participants. Who are the powerful NPC's and organizations in the world, what are they up to? I'd usually try to create layered plots, where the players might interact with a henchman of some shadowy figure at the start, and gradually get deeper into the plot as they went. Another useful trick is to have multiple versions of plots: Maybe the planetary governor is stealing money for himself, or siphoning it off to support the rebels, or is actually feeding it into your ultra-secret intelligence service who's keeping that detail from you. By having a couple alternatives, you can choose an outcome based on the rest of the ongoing story (e.g., a strong rebellion has him siphoning it off to support the rebels, a runaway intelligence agency causes the latter case).

In an actively GM'd game that was sufficient, but in your case I'd then create a new network showing major paths through the plots. How could the supernova plot turn out? What plots might feed into it and flow out of it? What are some interesting one-shot events that don't connect a major plot arc? What preconditions make sense for them?

From there, I'd set the preconditions to each event (e.g., rebellion strength >50, science level < 10), outcomes of each choice (rebellion strength + 2, set 'super nova prevented flag' to true), script them up and let the player loose.

Another useful trick is to have multiple versions of plots: Maybe the planetary governor is stealing money for himself, or siphoning it off to support the rebels, or is actually feeding it into your ultra-secret intelligence service who's keeping that detail from you.

But I think maybe a reversed order would be better? Like you start with the major plot and then trigger smaller events (which can be used by other plots as well). So you have the plot where rebels try to, well, rebell and it triggers a governor stealing money event, but the same event could be triggered by the runaway intelligence agency plot. And I suppose the player should have the option to "investigate it further" and only then it would be revealed if this governor stealing event is connected to something.

At the moment I try a method of predefined major plots. Then those plots have branches/variants and could trigger various smaller events (plot related or generic). But I don't know how it will turn out yet :)