Knew Alynn would know, lol - Alynn, you're pregnancy's version of Wikipedia, there's nothing you don't know!!
Aw hun, sounds like you've had a proper rough time of it recently. It must have been hard because I imagine you can't help but grow close to someone in that sort of situation and it's not just like losing your job, it's much more than that.
I know it's not your job but can you not have a quick email/ring around to try and give people a kick up the bum? Use almost a jokey 'just a quick reminder' email or something?
If you're even half as supportive of your family and friends as you are us ladies on here then they'd be crazy to even think about letting you down. I've got every faith that they just forgot about the RSVP because there's no question they wouldn't be there for you.
Try and keep smiling, you'll have an amazing time on Saturday, I just know it
Us girlies will have to have a drink (mainly non alcoholic due to all these bfp's and pending bfp's) in your honour so we'll be there in spirit for you