one breast not being drained for 10+ hours

DS2 eats very frequently during the day.  Like every 30-90 minutes.  He is a snacker and especially cluster feeds in the evening.  And he usually only feeds on one side at a time, even at night when he goes longer stretches.  But the past couple of nights, he has slept 7+ straight hours.  So one breast gets fed off around 3:30 am and he refuses the second breast, but then the other breast is going around 3 more hours so at least 10+ hours without being drained.  Then it is superfull, obviously.  But I'm afraid if this becomes a habit, my supply is going to tank because of the less frequent emptying.  Would you get up and pump the other breast?  Or pump before bed?  Or just deal with engorgement?  Will this lead to a drop in supply?  I'm trying to maximize sleep, but my supply is the number one priority and I couldn't sleep after DS2 went back to sleep anyway because I was uncomfortable and worried.  I'm trying not to become a slave to the pump because that will happen soon when I go back to work and I hate pumping (I already do it once after the first morning feed for a freezer stash).  Going up to two pumps a day on maternity leave seems a little excessive.  I never had this issue with DS1 because he never slept stretches longer than 5-6 hours and he always ate from both sides.