But to what extent, and at what cost to human society in the lower 48? The maggots will take care of the dead quickly enough; the weak will likely die on their own.
It's a fine follow-up, but note that your first question was what contribution grizzlies make to the ecosystem.
If you then want to go into cost-benefit, there are a host of additional questions. An example of what can happen with too many herbivores: spread of unwanted disease is enhanced. Ever hear of brucellosis? Well, a sick bison is a prime candidate for predation. Predators will target them and kill them before they infect a lot of others.
I mentioned one of the problems here out East: too many deer. People have been hurt and killed hitting deer crossing the road, and deer have become a nuisance to both homes and "wild" areas (though what passes for wild here isn't quite as wild as out West).
In essence, the question is one of ecosystem health. If you take out the top predator(s) in any ecosystem, the ecosystem will be out of whack. That can also have detrimental effects on nearby human populations. It's also one of the prime arguments for the reintroduction of wolves in many areas.