you have put this on the UK section but used the words DEP, so am assuming you are asking about the US Navy.
As for you going on vacation the destination would be the issue to be honest.......my son was in DEP for the USAF and wanted to go back to the UK for a holiday before he went to BMT, the recruiter whilst not banning him from going strongly suggested that he did NOT go as this was not always the best idea, at least 2 others in his DEP programme had been washed out due to something that happened on vacation and came back to bite them in the butt......So basically where are you thinking of going and how close to your ship date are you talking about.