You've got to feel for those caught up in it, but not a terrible lot could be done about the delays. It's all incredibly unfortunate that multiple problems came together on one of their busiest days.
There was a fatality near Lille late morning/lunchtime which caused severe delays, a failed train in the tunnel and OHLE problems in the other tunnel which meant single line working had to be implemented for some of the tunnel. Trains backed up, became massively delayed and it's difficult to make up time with Eurostar. You can't really miss stops or minimise turnaround times without cancellations. Some services were 300+ minutes late.
Then of course, there are no real alternative routes. (Some would argue Highspeed to Dover, boat over and then onward, but that means more expense for passengers, would take forever and there were ferry delays too). The lack of alternative routes meant that people just had to wait... and wait they did. St Pancras was like a cattle market, queues of people waiting for services, which isn't ideal when service resumes.
There is then the issue that the last services would normally leave St Pancras just after 2000. A possession in France overnight means that the last train must leave at 2130, otherwise it won't get through. If you have a train that you know will not leave until 2200 because it's so delayed, there isn't much more that can be done than cancel it.
All in all, a fairly chaotic day for Eurostar.
P.s Squaddie, good luck to your colleague! 6 hours delays via Euroshuttle and probably delays on the ferries from people abandoning the tunnel and using those instead!
We still got all our first class food and drink, too. 