It's a one night thing, but Hawke wouldn't mind waking up beside Isabela in the morning, or every morning. It may not be love, but every minute spent together is delight. It's the pleasure Isabela takes in simple things, like guessing the colours of Fenris's smallclothes, and the way her laughter rings joyous out. It's the way she goes for what she wants – be it through picking locks, or bluntly charming come-ons.
Hawke's not bringing feelings into this, no. But if it were something she were to stumble into – well, there's no-one it would be more fun to fall with.