I think the US has not yet defaulted on federal debt, so it seems people do get the money back, and hence the question is based on a false premise. 

I see no reason why the economy would grow after debt forgiveness, unless you assume the debtors would be able to get new credit, which seems unlikely. After all it will just be forgiven again. As for debtors being able to spend money on consumption and investment rather than interest: This was still spent when debt existed, only not by the debtors, but by the creditors who got it.

On a side note: I like your attitude. Would you mind lending me money?