Is it permissible to reject a suitor who is religious and of good character, simply because he wishes to live in his war-torn country? And would accepting to marry him be considered casting oneself into destruction?

The fundamental principle is to accept a suitor who possesses good character and religious commitment, but it is not absolutely obligatory to marry him. The Prophet, peace and blessings be upon him, rejected the proposals of Abu Bakr and Umar for Fatimah due to her young age, and he rejected Mu'awiyah's proposal for Fatimah bint Qays due to his poverty. Therefore, the command to marry in the hadith is to be understood as a recommendation. Among the valid reasons for rejecting a suitor are his intention to house the wife in an unsafe place or difficult living conditions, as this exposes her to peril and deprives her of her rights. However, if the place is safe and provisions are available, he should not be rejected merely because there is a war. If the suitor's intention is to participate in defending his country and in legitimate jihad, and the woman desires to aid the mujahidin, then accepting his proposal is not a transgression, with the understanding that the verse "And do not throw yourselves with your own hands into destruction" forbids abandoning the obligations of Allah that lead to punishment.