Looking at the questions and answer to these two questions. Why is the Burrow so cramped on the inside? & Why are there "dilapidated" buildings in Harry Potter? and neither mentions the longevity of magic. I recall several instances of magic failing to last; the money that was spread at the big quidditch game and the broken Cabinet that Malfoy worked on. If I recall correctly when Voldemort died, the curses on several people were lifted. I don't recall if any other spells fell apart with his death.
Is there any canon evidence on the the length of time a spell will live?