C-elms are damn near impossible to kill unless you let them get bone dry. They sprout roots quite easily. *I ran into a situation this spring simular to yours. I found a large elm [20" diameter trunk] that had been chain sawed right to the ground. It had budded at the top of the cut several years prior and produced a nice 4" diameter "new leader" with great taper and movement. I was able to saw this off hoizontal and then down through the root to preserve one little scraggly *feeder root about 3 foot out. I burried this deep in the growing bed, *I just checked it today and it's putting out new buds like crazy which means it's making new roots below. Latter on I'll air layer or ground layer to the section of trunk I'm after.
Chinese elms are like those potato chips. You can't have just one. Get plenty of growing space and pots on hand becuase before you know it you'll have 50!
Tony