Do dead coral skeletons leach/provide calcium to the tank?

[StephenRU]

If you leave a dead coral skeleton in the tank is that bad?

[PirateToast]

No, basically the same as rock at this point.

[OldReefGuy]

to answer your subject question, yes they will leach, but slowly over time and not real a measurable concern.
As Pirate said, treat them now like LR (which also leaches calcium)

[bnumair]

in order for dead corals to leach/provide back in measurable quantities pH has to drop below 7.7 which will pretty much wipe everything in you marine tank.

[Ron Reefman]

And what bnumair has described is how a calcium reactor works.