Hello everyone, I'd like to chime in and say that in my experience from 44.08-10 extinct civs did indeed seem to prevent any raiding altogether. It was really disappointing.
I wanted to played with modded elves (to get a 'fortress' full of immortal badass warriors conquering the world with wooden sticks and stolen copper, iron, and steel), I consistently couldn't get an embark from dead civilization to send raids - of seven different dead-civs I generated at the time no squads (6 of starting 7, in all possibly combinations) sent to 1 (one) local tile away (that is, literally a stone throw away) dark pits have returned in reasonable timeframe of 1 year. I tried to use vanilla raws to ensure it's not modding-related problem; no cookie, same result for all four worlds I tested.
When I tried regenerating worlds with same seeds (not perfect method, I know), it went that way: simply aborting generation while civilization is still alive allowed sending raids no problem and they're instantly back to my 1x1 embark started near goblins (or get caught and report losses correctly), but once they're extinct past year 17 or whatever, I couldn't get anyone returning anymore, ever, no exception, 100%, stuck on travelling. And yes, I read legends for those worlds and the lost dwarves, elves, whatever - they are 'in travel limbo' and don't even become refugees after outright abandoning fortress, nor do they arrive to destination past 5 years. I wanted to submit a bug report for this exact issue, but I kind of got distracted, forgot about it and cleared all saves after running out of space. I'll probably reroll several new dead civs for 44.12 to add to the bug report when I'll have time.
(Also, I recall having severe issues with pushing civs into the extinction which annoyed me to no end so I preferred to keep rerolling hostile worlds several times per hour until playable civ died on their own, but that's another issue)