Can a disbarred Illinois attorney write a legal contract in PA

Under the facts of your question, whether the attorney was disbarred in Illinois is irrelevant. You should focus on whether the attorney is licensed in PA. If the attorney is licensed in PA what happened in IL does not matter since each state licenses their attorneys separately. Any person can write a contract on their own behalf, so if that disbarred attorney has created the contract for himself/herself then not being licensed is also irrelevant. To determine if the contract is legally sound in PA, you should consult a local attorney who is licensed there.