I remember within the last year, authorities in KS and OK were working with BTK's daughter on some cold case murders/disappearances during the time he was active but also during the time he is not known to be active...
Never really heard any updates though.
John Douglass who helped develop the FBI profiling program in his book about BTK hypothesized that Rader found some other outlet when the murders stopped but others think he may have continued killing, just not in the wichita area.