hahahahaha, speaking of evolving.....
it is a running joke with my co-workers that my great-great-great-great-great grandkids will have only molars, no need for incisors   
;D

Evolution away from a meat-based diet would likely only occur very gradually, where meat sources are sparse and when dealing with an already (partially) omnivorous animal. The transition from carnivore could potentially be made, of course, but it would take quite some time and I imagine the chances of extinction would be higher. The Panda has had some trouble with this adaptation...

The following is from wikipedia, not always reliable but rarely flat-out wrong:

Despite its taxonomic classification as a carnivore, the panda has a diet that is primarily herbivorous, which consists almost exclusively of bamboo. This is an evolutionarily recent adaptation. Pandas lack the proper enzymes to digest bamboo efficiently, and thus derive little energy and little protein from it.

I would venture that that, along with the huge human component (deforestation ETC.), may have something to do with the species' current difficulty. The panda essentially carved out a niche for itself by specialising in a rarely eaten but rather abundant food source. More here from another site...

So while bamboo stalks and roots make up about 95% of its diet, the giant panda also feeds on gentians, irises, crocuses, fish, pikas, vines, mushrooms, rice grass and occasionally small rodents.

This goes to show that animals will essentially eat what they can get, but most are prevented from doing so because of specialized dietary requirements and the restrictions of their habitat.

Another misconception about evolution is that what an animal IS eating is what it SHOULD be eating (or rather, what it would most benefit from). Nature is highly competitive, and animals carve niches wherever they can. Watch any documentary on rain forests to witness the WILD level of specialization most living things have.

Just a note that ecosystems generally require predation of some sort, whether we are talkign about animal predators, bacteria, fungus (there's one that infects ants and uses their nutrients to grow), or even plants (Venus Flytraps, for ex.). Life thrives on consuming life, and without predation there would be problems with herbivore numbers (until they devour their food source). And of course, herbivores have their own prey (though far less mobile).

Now as humans, we are lucky, because we have pretty adaptive dietary requirements and the choice to eat in many different ways. Though sometimes I do wish we just couldn't digest animal products (though if that were the case, our prehistoric brains may not have developped). It would make the argument for veganism so much easier! Not that meat is "good" for people... but we sure can cram it down.

That is a distinct probability.