Nikola has not left the Sanctuary. Nor does he intend to.

As far as he's concerned, Helen had a fit of temper, causing her to react rashly and foolishly, and when she's had a chance to calm down, she'll either forget all about it or apologize, and they can get on with things.

Really, he's being generous in his assumptions because he thinks her concern for Ashley will finally result in her acting in (what he assumes) is Ashley's best interest.

And if not...

Well, for the moment, he's holed up in his lab, and he's jury-rigged a pretty impressive lock/barricade to keep people out. He'd really like to see Henry try to get through it. (Or John. He'd really like to see John try.) He can stay for quite some time without needing to leave for supplies, and if anyone really needs him, there are certainly ways to communicate that don't require face-to-face interaction.

So he waits.

Nikola is getting rusty.

But he has a good enough memory that despite the fact that it's been a good twenty years since he sat down at a piano, he's doing a fairly decent job of making his way through Au Claire de la Lune.

He doesn't play well, but he plays with great expression.