If they cannot handle the grid power being pulled due to load shedding, they have no business handling critical applications.

In particular there is no way you can predict when a backhoe will take our your power line. (Even if they call to get lines located - sometimes the mark is in the wrong spot, though most are they didn't call in the first place). There are lots of other ways the power can go down suddenly and nothing you can do about it except have some other redundancy.