It looks like Greece will be one of the first countries to reopen to tourism......
https://beta.ctvnews.ca/national/world/2020/6/2/1_4965433.amp.html
Of course for those of us from North America the main issue may be flight availability. There may be more connections and layovers, at least in the beginning. It appears that air travel within Europe is also getting back to normal to some extent, as easyJet has announced that they hope to open 75% of their routes by July.