I accidentally put vinegar in béchamel. Any salvation?

It probably tastes absolutely delicious. Nothing wrong with vinegar in your bechamel, unless it's curdled.

Toss it and call it a lesson learned.

Accidentally in place of what? I know you didn't ask, but bechamel for asparagus seems so heavy.

Well. you're screwed. You could save it by making it a riccotta cheese type thing for a mini lasagna cooked in a cup container if it makes curds.

For the Asparagus. A good sauce is Mayo, Lemon Juice and a if you have horseradish. that's good too. Especially if it's broiled Asparagus.
Broil asparagus tossed with a vinegar dressing.

And if have wassabi...make a wassabi mayo sauce for it.

I think there's no fix. Does it taste bad? You could call it eggless Hollandaise.