Get back hyper-v VMs after in place reinstall of host OS

If you have the files, both the vhd(x) and the machine vmx file, and your system is configured the same with similar vSwitch names then you should be able to use the command Import-VM -Register path\to\the\file.vmx.

If you no longer have your VMX files then you should just re-create a new virtual machine and when asked about adding storage, use the existing vhd(x) files that you already have.