How long does it take eggs to replenish once they spawn? I see guys catch bass or crappie up in the summer and say they still haven’t spawned because they are full of eggs. I’m wondering if they just grew the eggs back? If the nest is destroyed because of water level drop or predators can they grow them back and re-spawn? I can’t find any data on it. 

They don't replenish. Mature females begin forming eggs sometime around early-mid fall. These eggs grow and begin "ripening" (developing) the following spring with warming water temps and increased daylight length. Not every fish spawns, or gets to release its eggs. Those that don't reabsorb the eggs back into the body until the cycle begins again in fall.

There are also late spawners, I've seen spawning fish in June.  The "spawning period" is only for reference, there is no hard set clock-in-clock-out time for them.  Those fish are probably just really late.

 

Also, the spawn happens during different months for different parts of the country.  Southern USA can start in early March, while Northern USA can start in late May.

Also alot depends on body of water and water temp. Case in point the gravel ponds I fish most often the fish are done..every bass I've caught has Bern spawned out for weeks. Talked to a guy last weekend that said the week prior he caught a nice bass in another gravel pond only miles from mine that was full of eggs. That pond has several springs and the water temp is consistently 6-8 degrees colder.

Good excuse to post another link to this gem:

 

 

I've read/watched/ been told(source: bassmaster.com) that the females don't drop all there eggs on one bed, in case that bed fails.