The thing with the mindset for Magus, is he's always prepared for, and attuned, to death. After his many years in devotion to gaining power, he'd probably already come to terms with the fates of Schala and Zeal. Otherwise, he might have had the idea that perhaps he could sever Zeal's connection to Lavos in the hopes of saving Zeal, rather than just putting her out of her misery by ending her life. While he may feel some regret, or even remorse over the events involving Lavos and the destruction of the kingdom of Zeal, part of his acceptance with this lose is that these deaths occur in their proper time frame. Crono's death, on the other hand, is untimely in more ways than one. He has an established value in the war against Lavos, while (at least in terms of CT's story alone) Schala, had more or less done her part.
The three dot pause is probably more akin to jealousy than regret; that Crono has those that value him so highly, while he himself, (Magus) really isn't, or at this point, won't let himself be.