Do we even know what Capcom's expectations for Zack and Wiki were?
I remember reading about 420k for RE4:WE and 620k for RE:UC (more or less) but I don't remember seeing anything for Z&W except a US rep saying that it was meeting their expectation so far.
Also, while I doubt that it will sell as well as the RE games I think it should sell enough to make a small profit as it started very slow but seems to creep slowly up so it could do like 150k in US and the same or more in EU (as we love adventure games over here) and if Capcom was smart and kept its budget under a tight leash (if they wisely expected it to be niche title) it should be enough for it to break even.
Anyway, as long as it is close to breaking even the second one should be profitable as just like with the Phoenix Wright games they can just reuse the same engine with small improvement to do the second one and just tack on the story so that its break even point will be even lower.