My experience has been that if I plant plants, the tops die and a new top grows. So now I only plant bulbs (they're cheaper) and I do it in the Fall, although many people in my area plant in the spring. But I want to get them planted before the ground freezes solid as I never can figure out when to plant in the spring. Its a personal problem.
Mine have been a couple inches tall for a couple months now and they look fine. They have survived nights with temperatures in the teens and a couple feet of snow.
I think your onions are fine but, if you want to make sure, dig one up and check the bulb. It should be hard and smooth, not mushy. More important, did you plant the right kind of onion for your area?