I've had a really bad experience with doing trauma work right before my T left for holidays a few years ago. It led to a very serious bout of cutting for me, so your fears about not wanting to start trauma work when you know he's going to be away are valid. Have you talked to your T about them? You may be able to find a way to do some trauma work but then also work on containing the feelings it brings up so that you're not left hanging when he's away.