What did Yaakov have in mind when he said that, "whomever Lavan's gods will be found with him, he will die"?
Seforno: He thought that it was one of the slaves who had stolen them in order to worship them, in which case he deserved to die.
Rashbam: He did not mean literally, that he would die, but that he personally would punish the culprit - bodily.
Ohr ha'Chayim (to 31:31): Lavan's claim that he stole the Terafim lest they tell that he fled was plausible (Yaakov admitted that he fled). To counter it, he swore with a curse, like one who imposes Cherem amidst Safek.
Gur Aryeh: We know this was the cause, for otherwise, when was the word of the Tzadik fulfilled?
Riva: Even though Lavan did not find them, the curse of a Chacham is fulfilled, even if it was conditional and the Tenai was not fulfilled (Makos 11a). Moshav Zekenim asks why Tzadikim, Tana'im and Amora'im cursed on Tenai. He answers that it is fulfilled unconditionally only if it was not possible to fulfill it, like here.
Why is it important to know that Yaakov was unaware of the fact that Rachel took the Terafim?
Seforno: To insinuate that, had he known, he would neither have had the audacity to deny Lavan's claim nor would he have cursed the person who took them.
Why did Yaakov need to say that whoever stole the gods will die? A Ben Noach is killed for any of his Aveiros, including theft!
Ohr ha'Chayim: He will not have a claim that Lavan gave them to him, or he took them amidst forgetting.
Ha'amek Davar: Yaakov was not so sure that none of his slaves took something else from Lavan, and he did not decree death for this, only for idols. One who intends to serve idolatry in Yaakov's house should not live!
QUESTIONS ON RASHI
Rashi writes: "'Lo Yichyeh' - As a result of this curse...." Was it a curse (that the thief should die at the hands of Heaven)? Perhaps Yaakov meant the thief should be put to death?
Gur Aryeh: If so, the verse should say 'Yumas' (shall be put to death). "Lo Yichyeh" means not that he should be actively put to death, but rather it is a curse that he should die on his own. 1
Gur Aryeh: If so, why not use the more straightforward term 'Yamus' (shall die)? It is a more refined expression to say 'Lo Yichyeh,' and not to mention death explicitly.
Rashi writes: " As a result of this curse, Rachel passed away on the journey." But perhaps Rachel died in childbirth as many other women did, and not due to this curse?
Gur Aryeh: Rachel was one of the Imahos, and the verse tells us of her righteousness (when she was granted a son, 30:22). We would have expected that no harm would befall her. The Torah is perfect; if it tells us that Rachel died soon after, it must tell us why.