...that which remains and is worthwhile will be absorbed.

It comes down to what one means by "culture". In my experience, derived partially from being an editor at (latest count) three different literary publications with an international audience and contributorship:

Culture = stories told = "that which remains and is worthwhile."*

In which case, I agree. It/they will, with the appropriate effort, be collected, preserved, re-told, and will survive. This is the bright shiny smiling face of assimilation: the one that integrates Anansi (to give one example) and Coyote (to give another) into the children's literature of the Euro-American "West" without dilution of the Bro's Grimm and others like them.

In short, it is called inclusive. It not only recognizes Campbellian archetypes shared across the face of the planet, but celebrates the different ways they are expressed, without excluding archetypes not shared.

In realistic appraisals of what might be worthwhile trade between interstellar cultures, what stands out as most valuable (and easiest to transport) is folklore and art. If we have anything of value to contribute to what you've called new diversity, if it exists in the universe, it is in the stories we tell, and the art we use to illustrate them. This in turn demands discovery and preservation on the one hand, and acceptance and assimilation on the other, so that we have the resources with which to trade when the time comes.

Yes -- there's music, too. All of the same reasons apply to preservation and assimilation. I'm not a producer of musical recordings, or I'd have emphasized them as much as I did literature. I am, however, a fan... and I wouldn't want to miss a note, regardless of where it comes from.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
[* -- e.g.: The differences among Anglophone (English-speaking and -writing) cultures in varied places like Britain, South Africa, Oceania, Caribbea and North America still can often require, at least, an occasional footnote -- yet they all enrich the language as a whole, and that's only English, and only as a "first language"! In large part, the differences emerge from prior, regional assimilation of pre-existing native cultures and languages which then should rightfully, IMO, be absorbed into English as a planetary language. Add to them the enrichment derived from writers in the remainder of the former British Empire for whom English is a second/third/fourth language -- India, Pakistan, Kenya, Uganda, etc. -- and of the short-lived but no less far-flung American Empire -- notably, the Phillippines and various coral atolls in the South Pacific. Once you've accounted for all that inclusion, you may understand what I hope to bring to the pages of the publications I help edit.]