The kids are going to be taken care of in the OP's scenario, dreamingbohemian. They have their no doubt perfectly able mother with them plus another adult who, although "elderly" (what does that mean anyway? 60? 70? 80?), is not described by the OP as in any way incapable.
The OP's husband hasn't made plans without ensuring that the OP isn't available. She isn't unavailable. He merely wants to fly out to join her two- yes, two, not 22 days later in order to experience something he is highly unlikely to get the chance of experiencing again.
My point is about "letting" people. Several posters have said that they would or wouldn't "let" their husband's do this, that the OP should or shouldn't "allow" her adult husband to do this. Several.
Would I go and miss the anniversary in your example? You bet your life I would.
If I'm sick and need help from my kids etc etc - well for one thing this case isn't about the OP being sick and needing her husband there, for another I'm a very firm believer in my kids not being obliged to care for me in old age/ill health, for well thought out personal reasons so I would say FFS go and watch the match love and give the boys a cheer from me too, but that's going a little off-topic.
And I go back to what I said earlier - the person who has never got a babysitter in so they could go to the cinema instead of being home with the kids, who has never used the creche at the gym, who has never left their child with a friend while they went to lunch or shopping or to a wedding, who has never left the kids with their other half and gone out with friends, who is with their kids 24/7 rather than ever doing anything for their own pleasure which doesn't involve children, they might have a reasonable claim with the accusations of putting a personal interest and oneself before one's children. I don't honestly think there will be a lot of those about though.
And finally - what makes you think I'm not an Arsenal fan!! :P 