One lens to think about this is the lens of species extinction [+]. The world is currently experiencing species extinction at a rate significantly higher than the background rate, due to direct and indirect human causes:

> In contrast to the the Big Five [mass extinction events], today’s species losses are driven by a mix of direct and indirect human activities, such as the destruction and fragmentation of habitats, direct exploitation like fishing and hunting, chemical pollution, invasive species, and human-caused global warming.

> If we use the same approach to estimate today’s extinctions per million species-years, we come up with a rate that is between ten and 10,000 times higher than the background rate.

> Even considering a conservative background rate of two extinctions per million species-years, the number of species that have gone extinct in the last century would have otherwise taken between 800 and 10,000 years to disappear if they were merely succumbing to the expected extinctions that happen at random.

[...]

> It would likely take several millions of years of normal evolutionary diversification to “restore” the Earth’s species to what they were prior to human beings rapidly changing the planet.

-- https://theconversation.com/what-is-a-mass-extinction-and-ar...

I tried to find a source for the claim of "several million years of normal evolutionary diversification" to restore the previous level of biodiversity. After backtracking through a few layers of citations, we find this pair of studies:

> Lu, P. J., Yogo, M. & Marshall, C. R. Phanerozoic marine biodiversity dynamics in light of the incompleteness of the fossil record. Proc. Natl Acad. Sci. USA103, 2736–2739 (2006)

> Alroy, J. Dynamics of origination and extinction in the marine fossil record. Proc. Natl Acad. Sci. USA105, 11536–11542 (2008)

The more recent of the two studies concludes the following:

> The new [marine invertibrate fossil record] data show that two biotic mechanisms have hastened recoveries from mass extinctions and confined diversity to a relatively narrow range over the past 500 million years (Myr). First, a drop in diversity of any size correlates with low extinction rates immediately afterward, so much so that extinction would almost come to a halt if diversity dropped by 90%. Second, very high extinction rates are followed by equally high origination rates. The two relationships predict that the rebound from the current mass extinction will take at least 10 Myr, and perhaps 40 Myr if it rivals the Permo-Triassic catastrophe. Regardless, any large event will result in a dramatic ecological and taxonomic restructuring of the biosphere.

-- https://www.pnas.org/content/105/Supplement_1/11536.full

In the event where coral reefs were killed, and all the species they support became extinct, in 10 -- 40 million years we might expect to find that biodiversity had recovered again -- perhaps unlikely to see reefs again, but perhaps something rich and strange.

[+] : reduction of habitat doesn't necessarily imply species extinction, although it is going to put populations that depend upon those habitats under more stress -- stress that they may not be able to recover from