These things won't replace search engines - but they may destroy them.
A search engine is nominally a way to find actual knowledge. A huge problem is that the Internet has been overrun by people creating websites which bear the same attributes as websites with knowledge, but don't actually contain anything useful. These chat bots are just an automated form of that. Clickbait sites will use them to generate plausible-looking faux content which will overwhelm the search engines.
But as far as replacing search engines ... how? When I want to learn some information, I don't want to read an article which looks like information. For instance, these tools can do things like describe the components of a chair - but they have no knowledge of what the actual function of a chair is, so if you dig into their description things will get odd. You definitely wouldn't want to build a chair based on chatbot results.
I think the real challenge for a place like Google is that the trashy part of the Internet is what pays the bills. They could invert the problem and attempt to derank things which fit the patterns too well, but those are exactly the things which pay them money. When a free-use user finds a decent paper on a scientist's weblog, Google doesn't make any money. Google makes money off the trash sites flooding the zone with heavily-padded derivative articles about the scientist's paper.