Well, if the CO & S1 are due "back on sept 1st", then they
should already be available locally this weekend to boost your
case.
Seeing your MP is a bit late; by the time a change of orders funnel
down the chain of command, it'll likely cause some other poor soul
to receive the 1-year attachment ... at an even more last
minute.
IMO You need to contact the appropriate higher people who can
directly aid you in arranging an operational contingency. Is your
Chief Clerk, or any Manpower-savvy colleague, around to guide you
on the channels?
An online search suggests something called the PMC (Personnel
Management Centre) to be seemingly supervising overseas postings,
but I've not be able to locate their contact number or source. You
might try SAFPSC (Personnel Services Centre) to see if they could
refer you on:
http://www.mindef.gov.sg/dmg/des/psc/contactus/index.htm
Here's supposedly how the SAFPSC & PMC liase with each other to
ensure the affected servicemen's next of kin are visited regularly
during their period of absence from home:
http://www.mindef.gov.sg/dmg/des/psc/welfare&serv/carevisits/nokgrant.htm
I also think it'll help your case if you could persuade a colleague
to replace you beforehand, albeit at a late hour. My own indirect
experience (also for Cresdendo) wasn't with a lengthy posting like
yours - more like for a fortnight or something - & Div Arty
left it to our CO, who left it to our BC, who left it to the two of
us corporals on who should go. I verbally pleaded with my friend to
"take one for me", since I had over a month of off-in-lieu days to
clear just before ORD. Thankfully, he said yes, so there was no
hiccup. If you can line up a replacement yourself, I don't think
the higher-ups care who precisely flies over, as long as someone
does.