HCA: Hermit Crab Association

Some sort of fly or another tiny insect has taken over my tank and might have led to the potential death of poor Sakura (or they could have fed on her corpse)

How can I get it under control? My fear now is that they are tunneling and potentially laying eggs on other molting crabs.

The flies you're going to get are ones that eat dead and decaying matter. There is no risk to the crabs and they may even snack on larvae and pupae.

How big are the flies? Color? Behavior? Are they outside of the tank at all?

They are tiny and black with oval bodies. Could be fruit flies or something similar. I've seen them outside of the tank in smaller numbers.

After taking out Sakura the number did seem to decrease dramatically so I might have to ensure there is little to no rotting matter in the tank.

Probably phorrid flies then, which means traps won't work. Look for little brown cocoons stuck to surfaces in moist places of the tank, I've had water bowls covered in them before. Drstroying those will help prevent more adults from hatching. These guys like rot and moisture, so keep up with food removal and maybe let the surfaces in the tank dry off a little. I doubt they'll stick around!