I wouldn't of left lead in this application through the remodel job to begin with; someday it's going to have to come out.
Replacing with PVC would of been a wise choice but given your circumstance they make a brass ring with a elongated turndown inner design that is about 3/4" and the lead can be soldered to the ring.
If this lead is old and dirty.......your chances of getting a good bond to the brass are slim to none. I've tried it numerous times and all that happens is the lead disentegrates with the use of more heat. GOOD LUCK
I'd let the plumbers come back and take care of it...
ABS closet bend