Silver colony GONE!!!!

QB decided to Spring- clean the apiary this afternoon.  Scraped moss off concrete base - well left some moss on as the bees like to suck it for water.
It isn't very warm but thought I'd have a little peek in the top of each colony to assess the food (candy and Nektapol). All colonies flying except Silver.
That was the colony where the Q laid drone and I found her wandering around on her own 2 weeks ago. The best thing, I thought then with my 45years of accumulated wisdom - Ha! ha!, was to combine Silver with Yellow "H" which also seemed rather weak. Anyway I left it too late.
Today when I opened Silver the hive was completely empty. Not even any dead ones. No sign of Q cells on the comb.
Now I've heard of this happening to other  beekeepers but this is a first for me.
I wonder where they went? Unless one of you lovely readers suggests otherwise I will assume they just mingled with the other colonies on one of those very warm days we've had recently. QBZZZZZZZZZZZZZZZz