If your vacation was two weeks or less, stay with 250. If 3 or longer, your levels are starting to come down below optimal levels, so start with another loading dose of 375-500mg. (Assuming you are talking about weekly administrations).
You say you have missed one week, therefore it is 14 days since your last Deca injection. The half life of Deca is around 14 days. This means that since its been 14 days since your last shot, 1/2 of that amount (125mg) still remains. No need to load. Just hit today and resume your regular schedule.
If you only missed a week it shouldn't matter on 500mg, the stuff stays active for quite some time. I'd continue normally but do your next jab maybe a day or two earlier than usual