If you want to continue to use DECAs to make use of a dormant set of coax cables, unplug the power inserter. If you have only one line running to the SWM, disconnect it at the splitter and put a terminator on the splitter. That should work. If you have two lines running to the SWM, disconnect them both from the SWM and connect them to each other.
It's worth noting that you need at least two DECAs to form a cloud (one won't work) and that if the DECAs are getting power from DIRECTV receivers (not from their own power adapters) you will need to buy power adapters to run them. The old PS18 power supply that used to be bundled with the DECAs isn't made any more, and the new EPS10 power supply needs a dongle that isn't sold separately, so the only option is a PI-21 power inserter (such is as usually used for a SWM-enabled LNB.)