My work threw me a surprise one. It was just in the afternoon, an hour tops, just a cake and some cookies. Some contributed to a group gift; some did their own gifts.
Since none of them are actually planning it, it isn't happening. You don't need to throw it. Scratch that...you shouldn't throw it.
You can invite them to your mom's if you want, but I'd make it really clear that you understand that they might not be able to make it. An hour's drive is a big commitment for a co-worker, in my opinion. I'd probably leave them off the invite list for that reason anyway. Sounds like they were kind of trying to get out of it anyway.
If you wanted, you could bring in cookies or something AND the baby after he/she is born - like a month or so after. Since you aren't coming back, it could just be a quick drop in.
ETA: for clarity