Did you ask the technician to repair it or tell them to replace only the keyboard? If there was logic board damage they should have spotted it and recommended repair or replace (unless you told them just to replace the keyboard).
If you asked them tor repair it, and they missed the logic board damage, they should make it good (not you). An advantage to paying for repairs by credit card (if you did that instead of paying cash/check) is that the credit card company will stand behind you in a case where you have a dispute with a vendor.
If you paid cash or check you're on your own getting them to admit they missed damage (you might offer to pay 1/2 of what they think they need now to repair/replace the logic board).
If this answer is acceptable please remember to return and mark it.