I think I agree with this response the most. Even if this person didn't feel much like being in a leadership position, that's still 15 years of real-world experience and accumulated talent they just threw away. Unless this person's code quality was somehow declining in spite of that, they just lost a huge resource.
It makes me wonder if the OP got their lines crossed about the lack of leadership thing being a significant part of the reason they got fired and/or there's a significant part of the story not being told here, like maybe the company is being pummeled by the effects of the pandemic and had to trim some of their more expensive employees (of which someone with 15 years of experience is likely to be) or something.