Yes. As that answer, there're some informal sentences like that in Korean: ending with nown or nown form, commonly in writing. (ex: "모두 이곳으로 모임", "많은 양의 가스를 방출") Plus, also there're another informal quention sentences that end with '은/는': "가장 적절한 것은?", "당신이 사는 곳은?"

If a sentence ends with "-중", add "-이다" or "-이야" to complete it. Same goes for those ending with "-것". These are common informal endings. 이렇게 세 명이 모여서 식사를 즐기시는 중(이야). => The three of us are gather here in the midst of enjoying our dinner. 내가 이렇게 좋은 성적을 받았다는 것(이야). => It is that I have received such a good mark. If a sentence ends with "-듯", or "-뻔", complete it with "하다", "해", or "했다". 서로 잘 지내 보갰다는 듯(해). => It appears they're trying to get along with each other. 길을 잃어 큰일 날 뻔(했다). => I could have gotten in trouble having got lost. 즐기시는 is an honorific form of 즐기는. You use it for someone older, superior, and so on. 아버지가 한가한 오후를 즐기시고 ... => Father is enjoying his afternoon of leisure and ... You are never supposed to use it talking about yourself or your own group. Your example's "즐기시고" seems to be referring to the speaker's own group, so he is being facetious. It is a light hearted jest between friends.