I think anyone would be a miffed if they were separated from their husband at an event. Wouldn't you be missed off is someone did that to you?
There are lots of events, not just Royal ones that require couples to separate. And Royals regularly do, eg Trooping of the Colour and Remembrance Sunday when the non forces wives watch from a balcony.
Their joined at the hip and clinging on to each other is frankly sad. I find it truly pathetic. But yes, it will be a challenge for M to survive the Coronation without a hand to hold.