Actually, a UNITA victory could have long-term effects in the region.
It may well retard independence in Namibia - that will most likely still happen but possibly not in 1989.
It'll also have effects in South Africa. Any UNITA military victory will also be a de facto South African military victory. It's hard to say how exactly this will affect South African politics, but it may make the hawks in SA (Malan etc.) more confident and, perhaps more powerful. This may mean the moderates who battled it out to succeed PW Botha (De KLerk, Du PLessis, and Pik Botha) are completely sidelined and a hardliner succeeds PW. This will have all sorts of consequences for SA.
At the same time, a Unita victory is also a Cuban defeat, which could also have some implications there.
EDIT: Obviously, the above thoughts refer to a UNITA victory from about 1975 to about 1988, or thereabouts.