And his reappearance at a ball in a very 'gothic' fashion.

Henry Tilney is not to be found.
JA tells us in CH:5

"This sort of mysteriousness, which is always so becoming in a hero, threw a fresh grace in Catherine’s imagination around his person and manners, and increased her anxiety to know more of him." :-D

In 'Udolpho' and 'Clermont', the heroine is separated from the hero for long periods of time with no contact or knowledge of his whereabouts.
The next she sees him is accidentally at a ball.

Catherine sees Mr. Tilney at the ball at the Upper Rooms.

"From this state of humiliation, she was roused, at the end of ten minutes, to a pleasanter feeling, by seeing, not Mr. Thorpe, but Mr. Tilney, within three yards of the place where they sat;*

Emily sees Valancourt at the 'fancy ball' at Madame Clairval.
"Emily surveyed the gaiety of the scene with a melancholy kind of pleasure, and her emotion may be imagined when, as she stood with her aunt, she perceived Valancourt."
He was dancing with a beautiful girl.

Madeline sees Sevignie at the ball given by the daughter of Madame Chatteneuf;
Says Sevignie,
'Good heavens!do my eyes really deceive me, or do I behold Mademoiselle Clermont (Madeline)'
The heart of Madeline vibrated to his voice, and looking up, she beheld de Sevignie.

Emily sees Valancourt dancing with another woman, and her mind was tormented.

Catherine sees Henry who;
"was talking with interest to a fashionable and pleasing–looking young woman, who leant on his arm, and whom Catherine immediately guessed to be his sister; thus unthinkingly throwing away a fair opportunity of considering him lost to her forever." *snort* :-D

A lot of 'Gothic' connection here. And as usual narrated by JA in so amusing a manner.