[He's thankful to get the sense that she isn't terribly serious, although he's certainly not putting it past her for the joke to become an actually considered option. So he responds lightly, half joking and half serious.]

I appreciate the offer, but let's keep that option as a last resort.

[Or a 'never' resort, but he won't push that point.]

For now, since they seem to just be observing, we can at least waste their time by doing nothing interesting.