10 years earlier than they would have been expected to die without catching COVID. From anything, not just the flu. All-cause mortality includes flu deaths, yes, if that's what you're asking?
In any of the places I've lived, I've never been to a doctor with suspected flu and not been given a flu test of some sort. Sure, I've gone in with something and been told "this is almost definitely not the flu so we won't test" but every doctor my family has seen over the years has done flu tests when suspected.
I can't speak for everywhere, but I know that from what I'm told here (was actually talking about the lack of flu with some nurses who worked in local clinics and hospitals in the area), those who had covid-like symptoms were usually given the covid test no matter what. But, if flu would have normally been suspected and there wasn't a strong indication it was covid (loss of smell/taste, known exposure to a covid-positive person, etc.), they usually also got a flu test just in case.
I'm not sure where the 50% came from off the top of my head, but I think the 73% is wrong (should be 63%).
My math: If there is a 1% chance of something happening in a given sample, there is a 99% chance of it not happening. So, for a set of N samples, you multiply 0.99 * 0.99 * 0.99... N times or 0.99^N to determine the chances of it not happening in any of the samples. 0.99^100 is about 0.37. 1- 0.37 = 0.63.