I had the same issue in 2011. IIRC, maybe 40% of my impeller blade material disappeared downstream.
I flushed and flushed, straining every drop that came out. Never collected a single bit of the lost impeller though, other than flushing, I didn't do all the other steps that you're planning on doing. By all means, do that stuff, recover what you can. I'm sure the Jake Raby tales of 'hotspots' caused by bits of unrecovered impeller blade and the potential disasters that can occur do sometimes in fact occur.
But consider this: I talked with a tech at a local place (Steinels Autowerks in Twinsburg, OH—they do a ton of Porsche work). He told me they used to flush in such instances but rarely if ever got anything back by doing so. And they'd end up having to send the customer on their way with new pump/thermostat/coolant and the caution that problems might occur. He said they never did. To the point where, according to him, they stopped even bothering to do the flush. He said it just hadn't shown signs of being a problem.
Again, by all means, do what you're planning on doing. If nothing else, you'll know you did what you could. But Steinel's approach—while arguably cavalier—does at least indicate that in a significant number of these cases it just doesn't end up being problematic. What percentage? No idea, but it sounded like they had employed this course of action (inaction?) many times without issue. And in my case? It's been 10 years and 50k miles. I stopped losing sleep over it long ago!
