You will be fine. If you can't walk by then there is something seriously wrong! Go have fun.
At 1 month post-delivery I was still sitting on a pillow and was bleeding. Not to mention the struggle with breastfeeding that left me crying every time I had to nurse. I had significant tearing and healing was harder on me than L&D. And if you have cracked and bleeding nipples that leak every time the baby coos, you aren't going to want to be all dressed up trying to NIP while not leaking over your nice dress.
The honest answer is that no one knows how you are going to be after delivery. Every one's experience is different. You could be one of the lucky ones who is able to pick up life like normal and be able to go to the wedding with no second thoughts. Or you could have a hard time healing and need to stay home. I think RSVPing yes, knowing you may not be up to going is your best bet. Especially if you guys are close enough with the bride and groom that they would understand. This is really one of those situations where you just have to wait and see. GL! I hope you are able to make it to the wedding.