Realtimetrains shows the normal timetable running on Monday, as per FGW's stated intentions. (There are many alterations prior to start of service but these seem over by around 0600.) A visit to the station yesterday showed nearly all track laying is complete, I believe the Sunday closure is mostly about demolition of the old footbridge.
The problem Tuesday just gone was trying to run too many trains through a limited layout - next Monday is intended to have the full interim track plan available, with Bournemouth - Manchester trains using P8/9/10.
Having said all that, if you were starting from Reading itself, and the worst case situation was that XC were still running via Reading West, it seems most through XC services ran all right this week, so if the situation went pear shaped over the weekend you'd expect XC would just carry on with this week's set up?