College loans

As long as you've been paying the loan (or it's valid deferral for some reason, including that you're in school; the important thing is, you're not behind), the lender has no grounds to go after your grandfather or his estate. Lenders look to co-signors for repayment when the loan is in default or late.

As to whether the death of co-signor allows the loan to be called early--you need to check your loan agreement(s). They will govern what happens in this situation.