So, if a guest operating system has ACPI enabled, it is possible to soft reboot the server (like, doing a cron on the host) on a regular basis, or as needed.
Firstly, get a list of running guests
This will give you an output of the VMs names and ID's. So, for the ID that you want to soft reboot:
virsh reboot 3
Where 3 is the guest's ID.