I agree with you in that Tovolar will stay for a while. I think he's the Werewolf commander that people have been wanting for a long time, and a fresh take on the Gruul colours - that card draw is very useful.
I feel like Prosper should go down for good after a little while (maybe a month), and I think Edgar is going to see fast decline in the time between now and the release of Crimson Vow, when his popularity will shoot up again. Wilhelt's popularity really depends on the quality of the zombies in Crimson Vow and how quickly he becomes viewed as overpopularised. I know that I, for one, get bored of commanders quickly when there are a lot of people playing them around me. I have less of an urge to build them because it seems less unique.