If Alexei is not killed in 1918 and is seen as the exiled Tsar of Russia, I would guess he could marry:
- Maria Hohenzollern-Sigmaringen, daughter of Ferdinand I of Romania and Princess Maria of Edinburgh
- Princess Irene of Greece and Denmark,the fifth child and second daughter of Constantine I of Greece and his wife, the former Princess Sophie of Prussia.
- Ingrid of Sweden, daughter of King Gustaf VI Adolf of Sweden and his first wife Princess Margaret of Connaught.