If you dropped a nuclear missile from space, would the components disintegrate on reentry? - And thereby render the missile mostly useless because it won’t detonate?

A MIRV/MARV from an ICBM is designed to negotiate reentry stresses like heat and turbulence. It will, assuming targeting is not interfered with or the reentry vehicles are not intercepted by missile shield systems, function nominally and deliver its payload to target with no issue.

An SLBM or such not designed for reentry from low orbit will burn up and disintegrate under the stresses inflicted on it, likely scattering pieces of its payload across a swath of whatever it happens to be over. They lack any kind of ablative heatshielding and will not be sturdy enough to handle that + the turbulence of entering atmospheric conditions at typical reentry speeds. Basically an extremely inefficient and ineffectual radiological dispersal device, assuming nuclear payload.
 
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