If all the ice on Earth melted, global sea levels would rise by about 70 meters (https://www.usgs.gov/faqs/how-would-sea-level-change-if-all-glaciers-melted). The planet would look something like this (https://www.youtube.com/watch?v=2ZJyzWds09w&t=106s). There would still be plenty of places suitable for human life.
That said, it’s hard to give a clear answer right now to your question about the safest places to live. So many other factors play a role—seismic activity, pollution, and even politics. Political situations can turn even the most comfortable spots into absolute hell.