Tyan S5512 Heatsink question

I picked up a Chenbro NR12000 combo option with the Tyan S5512WGM2NR motherboard. I just started transplanting the mobo into a tower case and working on replacing the heatsink with an active cooler. I found that one of the existing heatsink’s mounting pins is sheared off, and the threaded part of the pin is stuck in the heatsink backplate. I’m unable to get the piece out of the backplate… do I need to worry about this? the new cooler is a Arctic Alpine 12 CO. From the looks of it, I should remove the heatsink backplate from the motherboard, but that sucker is on there really, really tight.
I’m not really sure how I should proceed at this point… any tips appreciated.

I know you deleted your post, but for others:

The NAS Killer 4.1 mobo (Tyan S5512) has a permanently fixed backplate. Take a look at the list below to find a CPU cooler.