Yes, the sentence is grammatically correct.
The phrase "May God restore in folds all we have lost" expresses a hope or prayer that God will return to us (or restore) everything we have lost, and the term "in folds" suggests a restoration that is abundant or in layers, implying that the restoration will be plentiful or comprehensive.
Here are a few possible rephrasings:
1. "May God bring back everything we have lost, and more. Amen."
2. "I