Scroll will let you go beyond whatever that hard limit is once it's merged.
And before that it'll take up less memory. But remember that it leaves
things open on the elasticsearch side so its not safe to have tons and tons
of these. I don't know how many becomes unsafe though.
I'd probably do a search for 1k and if the total that comes back is larger
then retry the whole query as a scroll. But how many of these scrolls do
you expect? You might be better off searching for 1k and if that doesn't
get you everything telling the user they must narrow their search.