if a worker and gets sick for 2 months is the company obligated to give him his job back?

It depends.

In the US, if you work for a company that has 50 or more employees, you have worked there for at least 1 year, and you meet the requirements of a serious illness = they are required to provide you with the same or similar job if you return in 12 weeks. This is governed under the Family Medical Leave Act.

Some states have similar provisions.

In the US there is a law called FMLA ( see http://www.dol.gov/whd/fmla/fmla-faqs.htm for details) that guarantees up to 12 weeks of unpaid leave to eligible employees. To be eligible, you must have worked for the employer for at least 12 months, and the employer rmust have aat least 50 employees. You'd be guaranteed you job or an equivalent job. If you don't qualify for FMLA leave, no your job is not protected.