There is no "progress", so there is no loss. For every hash that you calculate (you might calculate millions of these per second), there's a small chance of solving a block. Each hash is like an entry into a lottery. Each hash is independent of the others, so nothing needs to be saved.

That's right. The calculators look at the current odds per hash (this changes from time to time), and from that calculate the average number of hashes it takes to solve a block. Then you can figure out the average time to solve a block based on your hash rate.