Protagonist post-ending lore question

One question I can't figure out how to answer for myself about the protagonist. I can always headcanon something but I wonder if there is more concrete answers:

Who/what are they after the game's events? (assuming that they remain alive when separated from Arthur permanently)

What I know:

\- they were experimented on by Red Priests to enhance their inherited adaptation to resist the wyrdness, ultimately to become a soul vessel for Arthur

\- when fused with Arthur's foredweller soul-aspect, they become a wyrdness-infused human with foredweller abilities (immunity to wyrdness corruption & red death, able to instinctively read foredweller text, able to achieve legendary levels of physical/magical skill quickly)

So when Arthur's soul departs from their soul/body, do they lose the foredweller abilites? What about the legendary physical/magical skill they gain, do those belong to them or to the arthur-foredweller aspect that leaves them?