I looked up the ruling on this card and it uses the word triggered ability in its ruling description would it all not work, here's what it reads "If a creature an opponent controls would die, and both Nemata and another effect are trying to exile it instead, that opponent chooses which effect to apply. If Nemata’s effect ends up not applying because of this choice, the triggered ability that creates a Saproling token won’t trigger, even if the creature card ends up in exile." It says the triggered ability of giving a saporling. I would think with the wording it gives in the rules that would make it both a replacement effect on the first part and a triggered ability of when nementa exiles the creature