Yes because they have to bring it all back up in phases so that they only face the load spike* from one interconnect at a time, which can take some time and can fail if there’s unknown damage like the GP said.
It really depends on the region though because almost all large hydroelectric dams are designed to be primary black-start sources to restore interconnects and get other power plants back up quickly in phase with the dam. i.e. in the US 40% of the country has them so it’s relatively easy to do. The hardest part is usually the messy human coordination bit because none of this stuff is automated (or possible even automatable).
* the load spike from everyone’s motors and compressors booting up at the same time
Presumably emergency phone comms still work(?) so they could issue instructions to do a phased (heh!) restart to avoid every fridge/air conditioner/whatever restarting at once. Not sure how successful that would be however.
There’s usually two parallel processes going on during a black-start: spinning the power plants back up to get them synchronized to the grid, and getting power back out to all the consumers. Power plants have breakers that disconnect them from consumers which they keep disconnected until independent connections to other power plants allow them to spin up their massive turbines and synchronize them to the grid. There’s also tons of other downstream breakers at substations which will be in various states of functionality.
The power plants with direct connections have hard lines and black-start procedures that get power out to the most important customers like telecom infrastructure, which provides the rest of the comms. In a real world full restart it’s going to mean organizing workers at many substations to babysit old infrastructure so cellular is pretty much mandatory.
And to add more fun, this time they're not dealing with a small number of individual power plants that can be connected with only some phone-call based coordination.
Instead, there are literally hundreds of smaller wind/solar installations. Some of which depend on rapidly fading cellular communication to restart. And some might need an actual site visit to throw on the physical breakers.
It really depends on the region though because almost all large hydroelectric dams are designed to be primary black-start sources to restore interconnects and get other power plants back up quickly in phase with the dam. i.e. in the US 40% of the country has them so it’s relatively easy to do. The hardest part is usually the messy human coordination bit because none of this stuff is automated (or possible even automatable).
* the load spike from everyone’s motors and compressors booting up at the same time