I was going to school at UMKC and had a ticket for this show. When I learned it was cancelled because of the roof collapse, I drove across the state and watched them in St. Louis the next day, June 7, 1979. I'd actually seen the concert at Kemper Arena in Kansas City about 9 months earlier on September 27, 1978. Incredible band.

I had tickets for this show and it would have been my first time seeing Yes, so definitely a disappointment for me. But, I think it would have been a bigger disappointment if it had happened the night of the show!

I did find this link with lots of details on the roof collapse. It does indicate no one was there other than maintenance people. The local promoters did try to move it elsewhere, but weren't able to.

sfailures.wikispaces.com/KemperArena,KansasCity,Missouri

The next time I had tickets for a Yes show was Oct 1, 1980 in Tempe, AZ, which got cancelled due to low ticket sales. It is not listed on here, and I found a listing at YesGigs, but it doesn't note it was cancelled.