Image Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA)/J. Hester, P. Scowen (Arizona State U.)
Because the Hubble was originally designed to be serviced by human astronauts aboard the Space Shuttle (which has since been retired), its lifetime is limited. Without repairs, it'll slowly deteriorate, and unless NASA plans a mission to lift it back up into a higher orbit it'll eventually dip lower and lower before crashing into the Earth around 2037.
But the good news is that in 2018, the James Webb Space Telescope will be launched into space and will replace the Hubble as the most powerful space telescope ever. Scientists will use it to study all sorts of distant phenomena — including the early stages of the formation of the universe and potentially habitable exoplanets that may even contain life.