Lamarckian Identities in PNG

From James B. Watson's chapter "Other people do other things: Lamarckian identities in Kainantu Subdistrict, Papua New Guinea" in Cultural Identity and Ethnicity in the Pacific, edited by Jocelyn Linnekin and Lin Poyer (U. Hawai‘i Press, 1990), pp. 17, 26:

The aboriginal peoples of Papua New Guinea’s Eastern Highlands are organized in autonomous polities, some with as few as one or two hundred members. Many if not most of these local peoples experience episodes of radical revision in their membership. Most groups are formed in a highly fluid sociopolitical field, intermittently marked by relocations, realignments, and the patriation of alien immigrants who have been expelled by hostile neighbors from their own lands elsewhere. Restless or disgruntled insiders split off to form new groups; refugee outsiders are recruited from time to time to reinforce the ranks of those remaining. To the literal-minded genealogist, the long-term kinship and continuity of each such group seem confused, even compromised.

A truncated local sense of history nevertheless contains the frequent events of fission and fusion. In spite of ongoing exchanges of personnel, a common and ostensibly continuous local identity immerses not only long-established elements of the community but, in time, the descendants of recent immigrants....

Over half a dozen languages are spoken in the immediate vicinity of Kainantu, and all the communities I resided in have close social ties to at least one community of alien speech. Often two or three other languages are represented in these linkages. Many communities of the vicinity have incorporated refugees who arrived speaking a language other than that of their hosts. With time, if the refugees remain, their original language may be lost, but probably not without a distinct residue of the sounds, words, attitudes, and cultural practices they brought with them. In some communities in the 1960s there were refugees or their descendants still speaking their original language, … resulting in their designation by the community (from Pidgin) as “hapkas” [half-caste].

What does this mean for language documentation and conservation efforts in the area? To whom does any particular language belong, and for how long?