A person who contributed to an employer Simple IRA but did not contribute the maximum before the employer terminated the plan, can he contribute to a traditional IRA to make up for that? If yes, how much can he contribute to the traditional IRA?

It's the same answer whether the SIMPLE terminated or not, as long as any money was contributed. As an "active participant" in the SIMPLE plan for, I'm presuming, 2001, his regular IRA deduction is governed by the income limitations. (Joint, if married) He could, of course, make a non-deductible contribution to the regular IRA. But in general, assuming he qualifies, he'd be better off with a ROTH IRA rather than a traditional non-deductible.