[CamaroRS92]

Ouch!
Had that happen to one window i was replacing the motor on once upon a time.
The spring does need to be there and needs to be fully tensioned or you will wind up ruining that new motor you just installed.

The good news - the spring can be re installed and tensioned fairly easily with a couple of big pairs of channel lock pliers and a friend to help hold things.
The Bad News- the whole window regulator and motor has to come out of the door to do it. The guide rails will all need to be removed and the top rail on the regulator that attaches to the glass needs to be seperated.
then you will have to work the regulator out of those tiny access holes in the door panel. You will definately need a friend to help hold the glass - it is heavy and awkward to hold and will fall like a guillotine and shatter if your not careful.
Lay the regulator unit flat on a concrete floor place the spring in the center slot and start winding until you get it fully tensioned an then slip the other end down over the post to lock it in place.

Good luck & be careful with that spring that sucker can slap the side of your head in the blink of an eye if something slips before you have it hooked in its final place

p.s - did i mention you will need a friend to help with this project