Are 2 tph (peak) Crossrail trains still due to terminate at West Drayton?
That is still implied by Crossrail's service details here, which were amended subsequent to the Reading extension:
http://www.crossrail.co.uk/route/surface/western-section/You'll see that West Drayton is the furthest station that gets more than 4 tph. I assume the 6 tph includes 2 short workings..
Also if the stairs from the subway close will the footbridge continue over the mainline so that during emergencies and engineering work so trains can stop at the Down Main platforms?
No, there are only two spans and three lifts shown in the approval. (Now that I read it properly - I forgot about the extra platform face on the new up relief...)
Planning drawings can be found on Hillingdon's planning website by searching for reference number: 31592/APP/2015/186
Paul