When I was in college, some group (not Cubans or other Hispanics) put up a bunch of posters that read:
¡CUBA LIBRE! ¡VIVA FIDEL!
I took my felt-tip and modified some of them so they read:
¡CUBA no sería LIBRE! ¡mientras VIVA FIDEL!
Everyone but the Cubans were angry.
The correct grammatical way is ¡CUBA no será LIBRE! ¡mientras VIVA FIDEL!
The former implies SUPPOSITION, the latter is an AFFIRMATION.