It's really frustrating when you purposefully make something that has previously been eaten and enjoyed, and then it is randomly rejected.
DSS went through a very fussy phase, he seems to be coming out of it now. I got through it by just sticking to his absolute favourite dishes, which is easy when he's only here for 3 or 4 days every other week, but not so easy when it's longer than that - I sympathise with wondering how you're going to get through the week!
Another thing that worked was not serving up a whole plate, but putting the pots/pans on the table and everyone serving themselves with what they wanted (within reason, e.g. he couldn't have all plain pasta and no sauce, but he could choose the quanities of each, or he couldn't have just roast chicken with no veg, but he could just choose one veg and not have to eat all of them).
My final sneaky tactic, if I'm making something I'm really not sure if DSS will like or not, is to tell him as I'm making it that I don't know if he will like it, maybe it will be too spicy/exotic for him...for some reason there is then more chance he will actually eat it! Though I have to say this can backfire and doesn't work every time ;-)
We would never offer an alternative dish, it wouldn't even be a possibility to be honest. Here (France) kids are expected to eat what the adults are eating, though not necessarily to clear their plate for the sake of it. The good thing is the stakes are less high, as there are generally pre-meal nibbles (eg saucisson, cornichons, crudités, nuts), bread always served with the meal, and cheese always on offer afterwards. So if not too much of the meal itself is eaten, at least they'll have eaten SOMETHING, not too much need to feel guilty about them going to bed starving. You just have to be careful that they don't gorge themselves on the pre-meal nibbles and end up actually not hungry for the meal itself. But re: the bread/cheese/healthy nibbly bits maybe you can adopt some of the French way of doing things?!