Well, there are no hard-and-fast 'rules', no-one else can tell you what you should do. you need to decide what's going to work best for you to stay more-or-less on the wagon long term. The diet is merely a tool for you to use as you see fit. There are guidelines, but they are simply that - the diet police won't batter down your door if you decide to deviate from them.
While having a meal a week may fit into your life better and that's great - it will give you a bit of breathing space, you won't see the meals as a 'failure', and may be more positive about it in the longer term. However you will also be breaking ketosis on a weekly basis. However if you mitigate it, and stick to high protein/low carb you may well get away with it. Your losses are likely to be a bit less, but in return you get a smattering of a normal life. Swings and roundabouts, innit. (It's kinda what I do a bit at the mo for assorted reason, but getting on and off the wagon more often than you need is really quite hellish, and it was, believe it or not, easier when I was in a position to say 'no' for weeks at a time. But it's my choice.)
There are also some events in your life you'll only have once, and not to enjoy them to the full (or to spend the day worrying and stressing over the diet) might be a wasted opportunity to fully experience an event you'll never get back. Alternatively, take a look at that list again - the one offs, knock yourself out - the others - try to surprise yourself, perhaps. There'll be other barbecues, for instance. Missing one is not going to be the end of the world, however think about how much fortitude you'll discover that you thought you never had.
The choice, (as well as the consequences) are yours. If it helps the diet work for you, rather than you throwing in the towel, then do it. We really can't tell you what's best for *you*. The short answer, is you need to work it out for yourself. But whatever you do, be accepting and at peace if it dents your losses for those weeks.
Good luck.
