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Active partition is on a failing HD

Th computer in question has a small SSD as c: where Windows 10 is installed. However, the 100MB System Reserved partition d: is (for whichever reason) on a large, old HD which is developing problems.

I tried to remove this HD, but then the system is no longer bootable at all.

Is there a way to make the system bootable from c: without having to reformat it?

Disk Management shows c: as Healthy (Boot, Page File, Crash Dump, Primary Partition)
d: appears as Healthy (System, Active, Primary Partition)