Eh it depends. When we had one of our subs locked there in protest we constantly received modmail from random google searchers asking to be let in so they can read random posts they found via google. The funny thing is many of those posts were things I had commented answers in. Makes me wonder how many of those google searches are now dead ends after the comment answer was deleted.

On the other side, back when I was a mod there I used to point people to earlier posts that discussed whatever question was being asked & sometimes people would complain that the earlier posts were useless since other people deleted their own comment answers in them. Even before Reddit protests people would routinely wipe their Reddit history, as a mod it was easy to see it happen in real time.

So overall people deleting their own comments does have some effect on making searches pointing to Reddit, or within Reddit, kind of useless.