Wedding RSVP question--etiquette enthusiasts come on out!

I would send him an email explaining your situation and ask if you can come.

I wouldn't because he may have invited someone else in your place and it would put him in an awkward spot. You did the right thing by declining when you didn't know for sure you could attend. Send a card, include a gift if you want, and wish him and his partner well.

I think you can send him a quick note and let him know about the situation. And just say, now hat I’ve got confirmation on my end I know I can make your wedding and would love to attend. But if you have already given your final headcount to he caterer and I cannot, I understand.

He sent you an email as he needed to know. I would absolutely not ask if you can change your answer. He probably either needed a final head count if the wedding is in early August, or sent a few more invites if it's in later August.

ETA  I didn't even think about seating charts.  Don't be that guest.

I would send a polite email with A LOT of outs given - acknowledging that head counts with location/caterer may already b e finalized, etc - but let him know that the dates for the work event were up in the air and now that they've been confirmed, you would love to attend but understand if it's impossible due to the late notice. I would make it clear that it was a work thing - so it doesn't feel like "better plans" fell through and now yo want to go, and again, give LOTS of outs for him to say no. But most events do have a certain amount of overage built in, so it may not be a big problem. And I think he'd be flattered to know you'd like to attend.

ETA: As soon as I posted, I'm second guessing myself. I'd send the email I described to some of my friends or closer former colleagues, but a "general" former colleague... probably not. I don't know.

Or even responded to the email with the above.  But once declining, it would have to be special circumstances for me to revisit.  Weddings are too stressful as it is without having to deal with an old colleague - save the drama for the family

Since the wedding is still at least 2 weeks away, I say contact the friend and change your response.

I guess I'd email and ask. If it's too late, he will surely tell you.

I think if he is a good friend and you want to be there.. he obviously wants you there hence the invite I would email explain give him an out and see.

Nope, I wouldn’t go there especially since he already had to track you down for an answer. 

I would just email and ask if it's too late and tell him that you understood if it was, no pressure.
We're pretty easy going around here, everyone would think you were silly for even bothering to ask.

You've declined. End of in my opinion. Do not send any emails saying you've changed your mind...smh that people think that's ok.