Into the Danger Zone? The risks of being in Israel during a time of war. When is risk-taking permitted?

Can you visit Israel during a war due to the danger?
How do hospitals deal with patients during missile alerts?
Is there an obligation to go to a bomb shelter while you are learning Torah?
Is it permitted to travel to and from Israel via Egypt, Jordan or Cyprus when Ben Gurion Airport is closed?
Can someone in Yerushalayim travel to Bnei Brak or Tel Aviv where it’s more dangerous?