On visa requirement.?

When you enter the United States on a student visa, you will usually be admitted for the duration of your student status. That means you may stay as long as you are a full time student, even if the F-1 visa in your passport expires while you are in America. For a student who has completed the course of studies shown on the I-20, and any authorized practical training, the student is allowed the following additional time in the U.S. before departure:

F-1 student - An additional 60 days, to prepare for departure from the U.S. or to transfer to another school.

M-1 student - An additional 30 days to depart the U.S. (Fixed time period, in total not to exceed one year). The 30 days to prepare for departure is permitted as long as the student maintained a full course of study and maintained status. An M student may receive extensions up to three years for the total program.

http://travel.state.gov/visa/temp/types/types_1268... ..

Continuing students who are going to travel outside of the United States must see their foreign student advisor and obtain an endorsement from the DSO or RO. The endorsement will be made on page 3 of the SEVIS Form I-20 or page 1 of the DS-2019. When returning to the United States, a continuing student/exchange visitor must present a valid SEVIS Form I-20 or DS-2019 with the DSO or RO signature showing that the student is active and in good standing with the school or program.

https://help.cbp.gov/cgi-bin/customs.cfg/php/endus... ..

As long as your I-20 is valid, you are in good shape in US. If your visa expired and you went back home and you want to come back to the US, you will need to apply for visa again with a new I-20.