At the singularity of a black hole you would not see a sea of quarks, because quarks have volume. The quarks themselves would be compressed down to just an infinitesimally small lump of just "matter".

Black holes can be "shut down" slowly. They emit "Hawking radiation" from just outside the event horizon. This implies that a black hole "evaporates", before eventually vanishing in a burst of radiation. The speed at which evaporation takes place depends on the size of the black hole, with smaller holes evaporating faster. I don't think they explode too violently. It's like boiling water - it can spit and bubble violently, but the last few drops go in the same way as the first did

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