my cousin got married on Wolverine's birthday, in Chicago. We were planning to go to the wedding when we thought that it was a bit later in Nov, but when we found out the date, we knew we couldn't make it. (If you recall, we had both my family and my ILs in town for Wolverine's b-day.)
We RSVPed "No" with a nice note, and sent a gift (check) a few weeks after the wedding.
The check was cashed almost immediately - very early December - and we have yet to receive a TY note. I know she sent them out because my mom got one in mid/late-Dec, and was telling me about it last night. Apparently she sent out photo postcards (in an envelope) that had a picture from their wedding with "Thank you" printed on it - nothing personal written, not even signed. That seemed a bit tacky to me, but at least she received an acknowledgement.
it's NBD, and I didn't really think about it until my mom mentioned their TY card last night. I'm not expecing anything at this point - I'm glad my cousin had a nice wedding, and hope she gets good use out of the cash.