Runner's Training Tips: Late marathon training schedule messed up - tactics

With just a few weeks left of the long runs before I taper for the marathon, work is sending me to Africa for 12 days. I've played around with my schedule and shortened weeks to do 18 miles the day before I leave (& 3 days before I normally would). When I get back I plan to do 20 (3 days after my schedule says). Now...the last 22 mile run would be the following weekend (3 days after 20). Do I continue with it the following week & then adjust the schedule, drop the 20/22 and put my energy into a single long run on the last weekend I'm supposed to or what?? Seems I risk injury either way.

 Ps. I definitely will not be able to fit in long runs while I'm away but may be able to fit 5-8 milers sporadically. Its likely I'll get some swimming opportunites too.