Two whole schools of mathematics died in "unfortunate and unfitting circumstances", namely the Lwów school and the Warsaw school:

http://en.wikipedia.org/wiki/Massacre_of_Lviv_professors

http://en.wikipedia.org/wiki/German_AB-Aktion_in_Poland

http://en.wikipedia.org/wiki/Stanis%C5%82aw_Ruziewicz

http://en.wikipedia.org/wiki/W%C5%82odzimierz_Sto%C5%BCek

http://en.wikipedia.org/wiki/Herman_Auerbach

http://en.wikipedia.org/wiki/Stefan_Kaczmarz

http://en.wikipedia.org/wiki/Antoni_%C5%81omnicki

http://en.wikipedia.org/wiki/Juliusz_Schauder

http://en.wikipedia.org/wiki/Stanis%C5%82aw_Saks

http://en.wikipedia.org/wiki/Stefan_Mazurkiewicz

http://en.wikipedia.org/wiki/Adolf_Lindenbaum

http://en.wikipedia.org/wiki/Samuel_Dickstein_%28mathematici...

http://en.wikipedia.org/wiki/Leon_Chwistek

http://en.wikipedia.org/wiki/J%C3%B3zef_Marcinkiewicz

Some members emigrated before or during the war and spread all over the world, mostly in the US. After 1945 almost none of the original members were still alive and in Poland/Ukraine.