Yes, but has it taken both OS’ out at the same time? It hasn’t but it could happen, however, the chances are even less. There’s obvious risk mitigation in mixing vendors in infrastructure for both hardware and software in the enterprise.

If some critical services were lost in your enterprise last time until RH updated their kernel then you could have benefitted from running that service from Windows as well. Now the reverse is true. You could have another DC via Samba on Linux in your forest if you wanted to, in order to have an AD still for example. Same goes for file share servers, intermediary certificate servers (hopefully your Root CA is not always on the network) and pretty much most critical services.

Most enterprises run a lot of services off of a hypervisor and have overhead to scale (or they are already in a sinking ship), so you can just spin up VMs to do that. It isn’t as if it is unreasonably labor intensive compared to other similar risk mitigation implementations. Any sane CCB (obviously there are edge cases but we are talking in general here) will even let you get away without a vendor support contract for those, since they are just for emergency redundancy and not anywhere near critical unless the critical services have already shit the bed.