Yeah well, I'm sure a lot of people wrote off Arakawa in years past too.
The difference is that Arakawa never took a year off from competition, much less two or three. She just didn't always qualify for the Japanese world team. (Same as Slutskaya didn't qualify in 1999.)
A more similar comparison would be Katarina Witt and Elaine Zayak returning in 1994.
Witt had been touring and competing as a pro during the 6 years since she had last competed. She came in second(?) at German Nationals, and second of the German ladies at 1994 Euros and Olympics.
Zayak had not been training at all for almost 10 years. She had to work hard to get back into competitive shape, qualified for US Nationals, and came in 4th (probably would have been 5th if Kerrigan had been able to compete).
Respectable results, but not on par with where they left off in 1988 or 1984.
There had been big changes in the sport between 1988 and 1994, primarily the elimination of figures and the increased jump content, that made it hard for those skaters to keep up with the younger competitors. In this case the big change in the sport would be the demands of the new judging system, but Cohen and Slutskaya had already had plenty of time to adapt to that.
But the primary obstacles would be the wear-and-tear these skaters' bodies have already put up with through their years of previous competition, including chronic injuries, and the difficulty of getting back into shape after not training at a competitive level for several years. Other strong skaters from the same country would also be an obstacle to qualifying for an Olympic team -- this would probably be more of an issue with the American than Russian ladies.
If any or all of them choose to make the effort, they may well be able to get back to a level where they are able to make a respectable showing in competition, and depending on what the competition does at their Nationals *maybe* qualify for the the Olympic team. Actually being better than or equal to all of the top skaters of 2010 and thus being in contention for Olympic medals is a lot less likely. If their competitive fire and physical condition are up to it and they really want to try, some good skating and interesting human interest stories may come out of the effort regardless of the result.