During the first job I had at a veterenary office, someone was paying buku bucks to keep this whole clutch of normal-colored cornsnakes alive. These were the tiniest most ungodly thin snakes I have ever seen to this day. I have a suspicion that they were actually manually removed from their eggs prematurely and somehow (don't ask me how) they pulled through. There were six in the beginning, and only three made it. One of these three was like.. An earthworm. The only thing small enough for it to eat was an insect every few days. It lived, but the quality of life to this day (if it's still around) I couldn't tell you. I am positive it is still an abnormally small snake.
I would think that if you fed a cricket very frequently, you'd be alright. The snake would have an abnormal metabolism, but since crickets are digested quicker than mice, as long as you kept up with digestion, I'd think that nutrition would be sustainant. Crickets are quite defficient in calcium, which is why lizard owners often use RepCal or other calcium supplements with them.
This is not common knowlege, but herps can actually develop soft, spongy bones from a lack of calcium. It is extremely disturbing to see, and even worse to correct. Once bone has already grown, it takes a considerable amount of time for it to repair itself, but it will if given the chance.
I'm not saying this would most definitely happen if you decided to feed crickets, but mice are definitely higher in calcium (and other nutrients) than insects, atleast for corns.