It appears that the riser is leaded into the hub of some cast iron. I think I'd try to remove that whole thing, riser plus drain from the hub. To build it back up again, you'd need to find the proper sized donut, then that should let you use a PVC riser and then any drain you want. There appears to be enough room to make that work, but you'd have to measure carefully the depth of the drain and how deep the pan is relative to the hub below.
To remove the riser from the hub, generally, it works best to drill a bunch of holes in the lead, then you can pry out the lead and then clean up the interior of the hub so a donut will seal well.
https://www.fernco.com/plumbing/donuts-o-rings/donuts
It's important to get the right size - while the PVC is standard, the actual dimensions of CI hubs is not. Just like Goldilocks and the porridge...you want it just right to work!