This depends - when is your study program ending ?
I studied in the UK for a masters program which ran from September 2011 to August 2012 - I was given a visa which lasted from August 2011 till February 2013 ( i.e 1 month before the program start date and 6 months after the program end date). My graduation ceremony was at the end of January.
I personally did not leave the UK, but quite a few International student friends of mine left the UK for a while, either to to go to their home country or got a schenzen visa to go around Europe. Most of them came back in the UK in time for the graduation ceremony - They used the same old Tier 4 visa.
So what I know I that the Tier 4 visa is designed so that you complete your course and have enough validity so that you can attend your graduation ceremony (or complete any remaining course requirements). It is also a multiple entry visa for the time period it's valid.
If your tier 4 visa is valid till when your graduation ceremony is held, then you should have no issues re-entering the UK. Just remember to carry your invitation letter to the ceremony. If you don't have one, ask your university for one.