I wouldn't worry about Kobo. Borders lost money this year. B&N lost money this year, but Chapters Indigo--which owns 59% of Kobo is flush. See
this article in the Globe and Mail from early December. If Borders goes out of business, the shares in Kobo would probably be the only thing of value they have to sell. The Kobo-Borders % was true at one time, but Kobo had a second big influx of money since the Bloomberg article. I have no idea what Border's share of Kobo is now.
@laughing dragon: I am assuming that since you have a Sony reader, you have downloaded from Kobo using Adobe or Calibre (for non-DRM), so you are good to go with backups. Let's not get all panicky about this.
The bigger issue for Kobo is that they may no longer have a US partner with bricks and mortar stores. Kobo readers are being sold at Best Buy, Future Shop, Chapters, and Walmart in Canada and I would expect that they could sell in similar ways in the US. The only difference would be that purchasers would connect to Kobobooks.com instead of Borders.