I asked for validation on a debt from a collection attorney and they sent me a letter back stating that they were not going to collect and had returned the debt back to the original creditor. So does this mean that the original creditor will sue now? Thanks

Evidently the collection agency feels the debt is "uncollectible"... they possibly have tried many ways to see you pay the debt and feel they would have more time on your file than its worth... to them.
Your debt is now back in the hands of the original ower. He may decide to sue... possibly in small claims court, if it meets that court's criteria or sue in other means.

I suggest, if you have honorable intention to fully pay the debt, you make contact with the client and work with him/them for some time and method to accept the responsibility.
Usually, they might reduce such payments----without added interest---to get the debt paid.

If this is an attempt to avoid payment of such debt, I wouldn't count on such success... card owners have a long memory.

It may very well mean that the original creditor doesn't have anything to prove the debt. Doesn't mean the original creditor won't try again either after it finds the documentation or just because they want to give it another try.

Creditor may not want to pay the Attorney to spend any more time on this.

The collection attorney may just make the initial approach and then the creditor uses an actual collection agency which charges a smaller percentage.

Hard to say - could be a lot of things.