Figured out how keeping him alive might work
put nicholas into the growth vat ASAP; researched vital monitors on the meantime; once he was 3 he could benefit from Le's preach health; all this + max quality glitterworld medicine tending might be enough to save him through the immunity meter (that is invisible without fucking dev mode? why).
I still think this shit is bugged; the "randomization" timer is in the negative 600k ticks, meaning a change from the "grave" type of illness should be 10 rimworld days overdue, whereas the wiki states that this change should happen once every 1-3 days. This is a bit ridiculous but I kind of enjoyed the challenge.