This is an interesting thread... good idea OP. Anyways, my thoughts:
Radio Shack: definitely a likely candidate. Personally, I live about 20 miles from Fry's and I have a Radioshack 20 feet from my front door. Guess what... I'll drive the 20 miles to Fry's everytime. And the sad thing is- so will everyone else I know around my neighborhood. I've been in that Radioshack once to buy some speaker wire when I first moved out here a couple years ago. Since then I've never stopped in. However, in areas where the only other electronics retailers are Best Buy and Circuit City, Radioshack is still a semi-viable option for those hard to find electronic pieces (transistors and other small doo-hickeys).
Blockbuster: Not a chance in hell they're going down anytime soon. THe last coupld of years the CEO has definitely made some questionable, if not outright retarded, calls. However, with their big push for the online market, the Big Blue has shown the major shareholders that they do, in fact, still have a very large push with the moving watching community. So while Blockbuster is losing money giving away all these free trials and free rentals, they are getting it back through bigger investments. The temporary loss is offset by the investments and once Blockbuster has a solid ground to stand on with the online community, they'll actually start turning a profit with it and can start making money for the investors again.
CompUSA: Definitely my first thought before reading anyone else's responses. They are so many things they carry that just never sell at a profit. Games and game systems don't turn them a profit. I doubt they make any money on the TV's. The only thing they possibly make money on is computers and computer hardware. But with BB's and CC's popping up everywhere, CompUSA is going to quickly fade into the shadows with higher prices than everywhere else.
FYE (and all other Transworld subsidiaries): Transworld owns all of the following companies- FYE, Coconuts, Wherehouse, Strawberries, Spec's Music, Planet Music, Saturday Matinee, Sam Goody, and Suncoast. Everyone has (or had) at least one of these somewhere close to them at one point. And anyone who has been into one knows how overpriced they are. Transworld has always been a company that barely makes a profit. I worked for Spec's Music in Miami, FL in 1999 right when they were bought by Transworld. Before the buy out, the only things we carried were CD's, tapes, and CD binders (and maybe a handful of movies). Our prices were higher than BB's, but only by a dollar or so. Once we were bought out, our prices almost immediately jumped up a couple dollars on everything. We started carrying all sorts of non-music related items to crowd the register area for impulse buys. We started pushing suggestive selling. It just seemed like the company was so desperate to make any kind of money that it didn't matter what we carried, as long as someone would buy it once in a while. So rather than relying on ticketmaster sales and CD sales, now we were relying on suggestive selling and some clueless people to help keep us afloat.
To cut the rambling short, I say Transworld is definitely on the brink, but I don't think they'll give up before CompUSA. We'll one or more branches shut down (just like what happened with many Sam Goody's), but the company will keep it's head above water just a little longer than CompUSA.