It's okay to leave the drain closed. Skimmers are more important IMO. Scoop, brush, sweep all you can to remove debris. That will also help the liquid chlorine. Yes, if you can get your hands on a sump pump to move water around until the main pump is running that's better than nothing. For now though, only pour about 1 gallon of liquid chlorine into the water each day and brush it around a bit.
Big question - Do you have a TF-Series (or Taylor K-2006C) test kit? If not, that needs to be a priority in order to start the
SLAM Process once your system is operating again. The proper test kit is key to ensuring a successful
SLAM Process. I highly recommend either the TF-100 or TF-Pro series (link in my signature), but the Taylor K-2006C is good as well.