It's not a question of "is it worth the risk" so much as "why does a civilization that can move faster than the speed of light to a distant star and drop in scoops capable of withstanding adjacent fusion reactions then perform high energy reactions to separate the finely blended elements care about getting a bunch of iron?"
Surely we could just...I dunno,transmute some or something
in answer to your question we're talking about timescales of thousands upon thousands of years when even we're in the "danger zone".
We've been staring at some "any day now" candidates for
decades and by any indication we could stare for centuries and still know nothing about the day or the hour.
I imagine if there were like, superfuturistic mining ships they could analyze the star every day and know months in advance, perhaps even down to the hour....but this is like worrying about supervolcanoes blowing up your mine outside of yellowstone. The odds of it happening in the given series of years that your ships circle around it are pretty low...unless you like, develop a civilization around that star, then things get fun.
...and obviously this would be a cool mechanic but once again we're talking about very specific stars, many of which are quite far away from us and cosmically quite aberrant. One in a million. I think that's probably why steve hasn't included a "supernova simulation mechanic" in the first place