Hi, I am not in Ukraine, but I was in Egypt when the revolution happened in 2011. I was working for a local company full time but I had a small contract on Upwork. I know how upsetting Upwork's email may seem but I can understand where they are coming from.
The day before the revolution, I told the head of our company that I thought there would be a revolution the next day. I could sense the mood around me, but she just laughed it off and said, "Nothing will happen tomorrow." As much as it may seem like everything is normal for you now and you want to believe and hope it will stay that way, things can change overnight.
Most of the work the company did was with clients overseas, the rest with people who left the country. The government shut down the mobile phone network and the internet 3 days later. The mobile service came back after maybe 36 hours but we had no internet for 5 days. Only landlines were working for calls, and not many people had landlines nor did we have eachother's numbers. Don't underestimate the possibility your network may get cut off.
About a week later we went to attend a protest. We had been warned by some well-connected people that the previous day's protest would be attacked with snipers. But nothing happened and so we went the next day. Well, things were pretty quiet but it seems the planned attack had been delayed and we suddenly say a huge battle breakout. Google "The Battle of the Camels" for more details. My boss knew I was going downtown as I had talked to her and she asked me to pass by our office on the way to make sure there was no damage to the premises as protests had passed by there a few days prior. She saw the attack unfold on the TV and called me to make sure I was OK as we were headed home in a taxi. So yes, your clients may worry about your safety.
Even by time I had internet again, I was not in a mental state to contact my Upwork client. When someone has tried to kill you and your family and the future of your country is up in the air, believe me you take a huge mental hit and you may find it hard to focus. I got dinged a bit in the review my client left but I didn't sweat it as it was a small job, but I would recommend at least keeping your clients in the loop even if it is simply to say hey I need to stop or I am continuing. That way if they do hold it against you in reviews you have a good justification to complain.
Finally I want to say having recently worked as a client on Upwprk, I passed on an application for a position from someone otherwise qualified because they were in Lebanon. I knew that they did not have regular internet or electricity, and even though it was simply as a writer, we could find people elsewhere that didn't present such uncertainty. I know that may feel unfair but this is a global marketplace and that's the price we sometimes have to pay for poltiical messes.
I've hired Ukrainians here on Upwork and they were excellent at their job. I sincerely hope for all of you there that things stay peaceful, but one thing I have learned in life (from the above mentioned experience and others), no matter how well you organize and plan your life and work, things can be turned upside down in a moment.
