I am currently a student in Germany. My Schengen visa expires on the 30th September, but I was planning to do a last trip to the UK before returning home to Mexico. The thing is that I would be entering Germany on the 20th and then traveling back to Mexico on the 29th. Would I have any problems when I try to re-enter Germany, as my visa will only have 9 days left before expiring?
It should not be a problem as long as your visa Schengen visa is a multiple entry visa. If it is single-entry, you will not be allowed to go back after leaving the Schengen area.