I wouldn’t worry at all about missing one session.
IMO a 9 day vs 7 day SD is much more important than missing several sessions.
If you haven’t already missed it you could do a little extra volume on the workout before the missed session to take advantage of the extra rest or just use the extra rest for recovery from your normal routine.
As for the weights just skip the weights for the missed session and pick up where you normally would have been so that you end your micro cycle with the proper RM.
Male: 51 years old
Bench Press 240 lbs. @ 178 lbs. (12 July 2012)
Power Squat 390 lbs. @ 180 lbs. (10 November 2012)
Deadlift 390 lbs. @ 180 lbs. (27 November 2012)
Total 1020 lbs. (finally made it 16 July 2012)