If you want to continue to live in the Northern Lines Seniority District, go to work there. The extra board guarantee should be pretty much the same. Your System Wide Seniority isn't any good up there, you'll have to start over if you hire out at any terminal other than a Northern Lines terminal and then transfer up there. They didn't buy into system wide seniority.
If you want, see if you can hire out at an old BN terminal. They don't have primary recall and you can leave as soon as you make a trip after class. Of course, you have to have a terminal that you can hold. Gillettte or Edgemont are good places to get your seniority established. Just look for the absence of "primary Recall" on the job vacancy announcement.