200K doesn't sound like a lot, but remember it's over 15% of the total audience.
I think it's kind of touch and go already, to be honest -- it's not doing as well as Seven expected anyway (I'm sure they'd have been hoping for about 1.5mil+), and Australia's Got Talent is doing better on a much smaller budget.
Part of the problem is they underestimated the audience -- the reason the US version hasn't been rating well is because they've been delaying it for so long and dumping it in a set of "special" two-hour episodes. By that point, everyone who's interested has already downloaded it. And it stands to reason that people who like the show enough to download one they can watch on TV would at least be aware enough to keep up with TAR Asia through the Wiki page, if not actually downloading it as well. I don't think it was a coincidence that the two episodes with the biggest audience drops happened right after the two episodes that were pretty much carbon copies of TAR Asia legs.
I also think that another contributing factor in the rating drop is the advertising by Seven. Episode 1 had the highest number of viewers, and in the week(s) leading up to that episode, there was a TARAus commercial in almost every ad break. Episode 2 also had a fair few ads, but after that, you don't even start seeing the TARAus commercial until Thursday or Friday, and loads of people probably don't see the commercial, if they don't watch Seven on the weekends.
Also, some of the commercials have been really great (such as Chris & Anastasia's massive argument in South Africa - I'm sure at least a couple of thousand people would've tuned in JUST for that argument, as I know a fair few people myself who would fall into this category). The commercial for Episode 7 showed Matt & Tom's passports and a policeman coming up to them - not very exciting stuff in my opinion. They could've maybe advertised the Farmers "lying" to the Models, or perhaps Dave & Kelly's ice-hockey pain, as that was much more exciting stuff.
Anyway, I guess we'll have to wait and see how the latter half of the season plays out, but I think this has been a great season so far, so my fingers are crossed for a renewal...