instead Resources Needed : Metal: 50 Crystal: 500 Deuterium: 250
put this Resources Needed : Metal: 25 Crystal: 100 Deuterium: 50
it will help much weaker players to put mines in big + after attack

http://i1097.photobucket.com/albums/g343/Akatcuki/Peinxd2323555.jpg

Or they could build fusion reactors which they can use in such emergencies,
or use the extra energy in the plus section to make up the difference when needed?

There are plenty of alternatives available,

The rebuild does need some extra work put in by the player, and not given to them on a plate
to ensure that they learn from their mistakes and avoid them in the future,
otherwise they will remain a farm forever