When Sylas heard that so many Portals had appeared in this small region, he wasn't sure what to think. But he knew that he at least had to go and check the region out.
However, going now, considering the situation, wouldn't be smart. Going now versus going later wouldn't make a large difference. If Cassarae was truly already on the verge of dying, his current self couldn't change much of that.
She had survived three months on her own before she found him, and she had survived this long without him, she would be able to hold on now.
He had come here for one specific thing: the Arctic King Cobra, and he had yet to find it. Only after he slayed this beast and completed the prerequisite he needed to clear his Quest would he continue onward.
As for the rest, these three gave him some assurance. At the very least, this portal wouldn't be actively pursued by any one group anytime soon. At least not seriously.