What was Big Willy Shakes going for?
Critics argue about whether or not Antonio is a just close friend to Sebastian or a lover. It's possible that he's both. There's no way to know for sure. Twelfth Night is famous for its gender-bending, cross-dressing, same-sex flirtations, so hey, a little same-sex romance isn't out of the realm of possibility in this play.
What we do know is that Antonio is pretty much willing to follow Sebastian wherever he goes. And that Antonio's "whatever goes" attitude totally fits in with the play as a whole. After all, this play is about stolen identities, long lost siblings, and some pretty hilarious gender comedy along the way.
That central message of play is exactly what Antonio is saying here: we'll just roll with the punches and be cool however it turns out. Sounds pretty daring and awesome, doesn't it?
To be fair, chances are Antonio has no idea what he's in for when he says "come what may." When he follows Sebastian into Illyria, Antonio ends up getting arrested for being a pirate. Then he accidentally mistakes Sebastian's un-dead sister for his friend and asks her for money. When she refused, he's hurt and alone. It's a bit of a mess.
But don't worry, it all gets sorted out in the end. And as you can imagine, Antonio's in for one crazy ride along the way. But hey, come what may. That's his attitude. And we're on board with that.
It seems that Shakespeare liked this phrase. It pops up again a couple years later in Macbeth. After hearing a life-changing prophecy from three witches, Macbeth demands to know where they got their information. They don't respond, but simply vanish into the foggy, filthy air. And then Macbeth says that he'll just have to wait and see what happens, so "come what come may" (1.3.146).
We guess Shakespeare liked his characters footloose and fancy-free. To a point.