I have to agree about "restart when someone dies".
Yes, you -can- lose everyone but Chrom and Robin and win (especially if Robin is female and they are wed). However, the question is "-should- you lose everyone?". There are 49 unique personalities total in the game (four not yet unlocked, though), and since they're gone forever in Classic... can you live with "I, the tactician, won, but I let someone die when they could have survived"? If no, reset. If yes, keep going.