This is hard to answer because scarcely any of us have experience of being utterly unneeded. There are different levels of resource trading in different types of relationships. Intimate relationships between the sexes are very much driven by our instincts to be about resource trading. A woman trades her youth, health, of which her beauty are indicators, for resources provided by a man in the form of labor, status and so on. Male-female relationships tend to be rewarding but also complicated and very consuming.
The simplest type of relationship is a good conversation with a stranger you will never meet again. Some of those relationships can have very high return on investment. The only investment may be a bit of time that very would very often be completely wasted on the phone anyway. No drama, no conflict, no potential fallout.
I agree but, are they fulfilling enough long-term to satisfy the needs? Will it be a driving force or a point of interest? It is an interesting question I think because as I see it, we need each other but if in some future we are fooled into thinking we do not, we may all live isolated in a group, none happy but none willing to make concession for others as that would mean conflict and a reduction of pleasure.
I don't think that kind of relationships can fulfill all our social needs. Not by any means. And I also agree that that scenario you present seems quite likely.