Comments can be nuked at any time and for any reason. They are "ephemeral". They are not considered part of the site content per se. This has always been the case.
If you need something that'll stick around a bit more persistently for an extended discussion about a question, pop open a chat room and invite the others to join. As long as the chat doesn't degrade into a topic that is unsuitable for the SE network as a whole, it'll stay up -- even if it's "off topic", as long as it's nothing illicit, the chat can stay.
If you don't need that persistence, then you should be fine with the comments being deleted.
And of course if you are producing constructive knowledge topical to the question at hand, you should attempt to include it in an answer (write one of your own, or suggest an edit to someone else's), or at least edit the question supplying the extra details the OP has provided.