So far the outbreak of hostilities has been somewhat contained. But on the edges there have been various smaller events that certainly could widen. This is not just the Russian/Ukraine conflict, but Israel and her neighbors, China and its disputed territories. I used to think that only select nations would experience war or rumours of war. However, now it seems that almost no nation is immune. That nearly every country has some looming problem that has reared its head. And those not directly affected are still typically allies of one side or another.
to answer some of your questions, I do think there will be food shortages, with some nations more affected than others. This could not only stem from war but from disasters like earthquakes, hurricanes, drought, etc. I think too we might be on the verge of a financial crisis. Such a crisis could see some nations currencies devalue drastically. (No, I do not see the dollar becoming worthless overnight, but other nations with weaker economies certainly could suffer far more.
As to missionary work, having lived abroad at various times, nearly all missionaries know there are risks. Some face far more than others, and I would assume that as God as called that they are faithful. God too can warn and move someone out of harms way. Those are individual decisions that each has to make with God. But in general, I think missionaries are at peace with their circumstances or they could not be effective. Most are thinking more in terms of souls rather than wars or other interruptions.
You are right to point out repentance and change can occur through negative events. So while times can be rough the outcome can be tremendously favorable to those that trust in God.
This verse seems to be the most applicable to uncertain times.
Isaiah 26:3-4 (KJV)
3 Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee.
4 Trust ye in the LORD for ever: for in the LORD JEHOVAH is everlasting strength:
Note that the Greek word for perfect is shalom in the original text, and the Greek word for peace is shalom.
So it could be read, I will keep you in peace, peace, whose mind is stayed on thee.