The Travel Agent landscape has changed, but the majority of agents/tour Ops have a 24hr phone line for emergencies, such as this. There is a lot of emphasis on getting through on the phone to either the airline direct or an agent or tour op on here, but in reality if you have booked through a decent agent or tour op, they will be very pro active in trying to sort things before a call has even been made/received.
It's not uncommon in situations such as this for a DR scenario to kick in and staff will be called in (a lot work from home these days) and the agent/tour op will already be aware of which of their customers are affected and they will be pro active in finding the best solution and then communicate same to their customers.
You are right that agents/tour ops have access to all available flights and routings (when compared to online companies) and they get immediate refunds if they need to change airlines etc.... It's not just flights that are an issue, if you are flying to pick up a cruise, that's another thing that needs sorting, accommodation and transfers are another - book it all with an agent/tour op and you get protection from the Package Travel Regulations and the agent/tour op sorts it all for you.
Of course some agents/tour ops are better than others, I know one specialist tour op that when there is a whiff of ATC issues, they respond immediately to cancelled flights (BA short haul are worst for this) and they change customers flights even before the customer is aware that it is cancelled either late at night or in the early hours of the morning.
Each to their own.....
