Colloquial English might say "if so, what then?" or "If so, then?" It does not always imply "what comes next," but simply "what is the situation?" and could easily include the idea of "how." It is closely related to the idiom "So what?" (How does it matter?) and is similar to the French usage "Comment ça?" or just "Comment?" (What did you say?)
It is correct, as SourireCache points out, that "comment" is not equivalent to "quoi"; and as Bennemann says, there is a difference in the meaning of the two words in English; but without context, the given translation is not the only possibility.