It is not explicitly stated what the king feels after Gulliver inadvertently escapes from Brobdingnag; however, we can safely assume a few things. It is clear in the text that Gulliver worries after his nurse's fortune with his departure, assuming the queen will be greatly displeased with her. As Gulliver had become something of a prized possession and display piece for the royalty of Brobdingnag, his departure would be very frustrating for them. He had been given a special box in which to live and was carried from region to region to show off to the people of the nation.
Based on Gulliver's distress at the dissatisfaction of the queen, coupled with his high place in society and the king's apparent dislike for Gulliver's account of England and human culture, it is safe to assume the king would be angry and disappointed at Gulliver's escape.