If a debt was paid by co signer in bankruptcy. Can the lender come after the primary as well?

Yes, Because you already paid the debt. Debt is one of the most stressful things you will have to deal with in life. It can be very draining and exhausting to be in so much debt and to feel like you will never dig yourself out of the hole that you have gotten yourself into. When you file, you will be discharging your debts and giving yourself room to breathe.

Yes. Its because you had settle your previous debt.

Yes, because the previous debt was settled already.