Well I just had mine fixed under warranty but his estimate was between $1100-$1300 to have it fixed. I drive my car hard and I did miss shifts occasionally but not often. My buddies went out at 20k miles while mine went out at 60k. So it is possible it is just a weak part. If it is factory warranty then they should cover it, no ?'s asked.
Nothing bad will happen to your car, just 3rd gear will eventually be useless (can't shift into it at all). I had mine broke for 7 months and I was still able to shift into 3rd just not quickly.
