In the interests of better communication, one language is the route we will ultimately go down as a species, I have no doubt. It will probably retain words from most if not all of the rest, but as the world grows smaller, so the ability of each of us to understand the others will grow greater.
The root language - the 'main' ancestor - looks to be English right now. Chinese may have the greatest number of native speakers, but it falls down on the written language. English is the most spoken second language in the world and is the official language of many international bodies, not the least of which are air traffic control and the scientific community.
The legacy of the British Empire, the dominance of American culture and the predominance of English speakers on the Web means that this overall trend is unlikely to reverse itself any time soon.
Not that there isn't a long way to go, of course. And there are many slips between 'promises to be' and 'actually attains' as Ancient Rome and medieval France - both the leading languages of their day - would doubtless attest
A kind of linguistic Darwinism is at work, which is the way it should be
