Is it true that if a woman is pativrata ,her husband can't die before her death. As even Yama can't kill husband of a pativrata stree.
This is what the Skanda Purana says.
Chapter 4, Kāśī-khaṇḍa (Pūrvārdha), Skanda-purāṇa
व्यालग्राही यथा व्यालं बलादुद्धरते बिलात । एवमुत्क्रम्य दूतेभ्यः पतिं स्वर्गं नयेत्सती ॥ ५५ ॥
- Just as a snake-catcher pulls out a serpent from its hollow, so also a chaste woman snatches her husband from the messengers (of god of Death) and takes him to heaven.
यमदूताः पलायंते सतीमालोक्य दूरतः । अपि दुष्कृतकर्माणं समुत्सृज्य च तत्पतिम् ॥ ५६ ॥
- On seeing a chaste woman from a distance, the messengers of Yama flee after discarding her husband, though he might have been a man of misdeeds.
न तथा बिभीमो वह्नेर्नतथा विद्युतो यथा । आपतंतीं समालोक्य वयं दूताः पतिव्रताम् ॥ ५७ ॥
- “We, the messengers (of Death), do not fear fire or lightning as much as seeing a chaste woman coming towards us.”
English Translation by G.V. Tagare
So, looks like yeah, the husband is safe as long as the woman remains chaste and loyal to her husband.
Although, few things to be noted:-
In case of Savitri herself, her husband died whike she was alive, it was only afterwards she got her husband back and alive, albeit through her "pativratya" only.
Take the case of Sri Krishna, at the very least, we must assume his eight principle wives were "super-chaste", but yet the Lord departed earlier and most of them later committed Sati or retorted to forests. So this maybe an exception.
In support, yet again, we have the case of Jalandhara and Shankhachuda who were basically involiable on account of their wives Tulasi and Vrinda. So, in this case, as long as "pativratya" of their wives was inact, the husband were safe and alice, even from Super-gods.