I had this happen once where I had to leave town for 5 days, 3 plants at 5 weeks into flower in 5 gallon buckets under a 400w HPS. So what I did was plan a sort of mini flush for them, unplugged my hps and set up cfls around the plants so they had less intense light(less intense light=less heat and higher humidty=less thirsty plants), made sure my timer was all good and when I came back the soil was still a bit moist. You might loose a little bit of bud growth time but once you switch back to the hps it'll kick back into gear. Also keep the fans blowing good as the humidity will rise as a precaution against mold and mildew growth.