Is my sentence 如果我没去上班就一起朋友去玩 grammatially correct?
如果我没去上班就一起朋友去玩


From my answer to this question Meaning in context


  it is a very common grammar structure
  
  [如果 X 就 Y] = [If X then Y]


[1: 如果] [X: 我没去上班] [2: 就] [Y: 一起朋友去玩]

[1: if ] [X: I don't go to work] [2: then ] [Y: together friend to go play]

The major problem is  "一起朋友去玩" (together friends to go play)

It should be "和朋友一起去玩" (go to play with friends together)

[和 + (noun) 一起] = [with + (noun)  together] is also a common grammar structure. And you can drop "一起" and write: "如果我没去上班就和朋友(一起)去玩" because it is strongly implied with the present of 和