Why might this derailment delay the overall project? The weekday possession area isn't affected, and they ought to be able to fix whatever is wrong by Friday night surely?
What follows is speculation as I don't know, but:
If there is any suggestion that the new / amended signalling was in some way at fault, and,
if signalling installation / testing was suspended as a result, and
if signalling installation / testing is on the critical path...
then the project will be delayed.
A lot of ifs there, and of course we don't know how much 'float' (contingency time) is in the schedule, nor what extra resources can be allocated to make up any delay, if indeed there is any delay.
It's fair to say we won't know if the project is going to run late until a full assessment of any delay, available resources and the remaining activities in the schedule has been carried out.