It depends on the reasons that it came loose (if indeed it is lose!!), and also what damage has been done by driving around on it - have you been able to check yet? it should be pretty obvious, if you grab hold of the damper and see if there is any play, and also watch it when the engine runs and see if it wobbles..
in all likelihood if it is the harmonic damper/balancer, and the woodruff keyway is shot, it could point to a thrust bearing issue iirc that due to excessive vibrations has caused it to come loose..amongst other possibilities of course.
but, no,if its that, this far down the line, a new pulley wont fix it IMO. It will be new crank and engine rebuild time.
Or a new engine Im afraid to say.
But still, you havent checked it yet by the sound of it?? so nothing is certain until the problem is identified