If I were in their shoes before the war, it’s much better to engrave the phrases in indestructible metal bars of any kind as it is resistant to fire, water or any calamity.
The detonation of a war bomb is incredibly powerful, and even if you store something in metallic form, I can assure you it will suffer physical damage, with the mildest possibility being that your seed phrase becomes illegible. In wartime conditions, it's advisable to leave the battlefield when feasible, as it's a matter of safety and also safeguarding our assets.
If you haven't considered how to securely store your phrase online, you're putting yourself and your assets at risk during such wartime scenarios. However, if you store it online, you shouldn't have to worry about your phrase once the war is over.
Note: Don't store the phrase in plain text. You can use a puzzle technique to make sure the phrase you create can only be deciphered by you. I believe that's a safer approach.
It is difficult to imagine if there was a war like Israel and Palestine. Maybe if you live in Israel, you can escape. However, I tried to position myself as being in Palestine with very heavy bombardment, maybe metal or steel would not survive if hit by a bomb. Apart from that, being in Palestine also means not being able to go to other countries.
One way is to actually save the seed phrase online, after which we only think about our own safety. Because in a war situation, your own life is the most important asset and second only to Bitcoin assets. By the way, we are very lucky to be in a safe country without war, I can't imagine being in a situation of war between Israel and Palestine.