Where did these choices come from? They are all a bit unnatural. Here is some general information about ways to express the future: https://www.ef.com/ca/english-resources/english-grammar/future/ I agree with Laura that "...he IS TAKING the week off" is more natural. Here is some information about using the present continuous for a (scheduled/committed) future arrangement. https://www.ef.com/ca/english-resources/english-grammar/present-continuous-future-arrangements/ I agree with Laura that of the four choices, #4 seems best. "He WON'T be here next week because he IS GOING TO TAKE the whole week off." "He won't be here ..." is a simple statement of a future state and "...he is going to take" is a plan. Here is more information about using "GOING TO" for plans and intentions. https://www.ef.com/ca/english-resources/english-grammar/future-going/ #2 is a bit awkward because of the repetition of "going to ... going to ...." "He ISN"T GOING TO BE here next week because he IS GOING TO TAKE the whole week off." Some teachers might argue that "he isn't going to be [at work]" and "he is going to take the whole week off" are both plans. OK, but I wouldn't say it this way (North American English). #1 and #3 "... because he WILL TAKE the whole week off" are wrong according to Murphy in English Grammar in Use. "will <verb>" is used for decisions but not for arrangements.

If I had to pick only one, I would pick #4. It's technically correct (I think #2 is, too.) #1 and 3 work but I probably wouldn't say it like that. Maybe they are technically not correct?? Instead of "will take" or "going to take" in #1, 2, and3, I would use "is taking." Then they are most definitely correct.

Hello, Arwa, I agree with Laura that #4 sounds the best, but in my opinion, the other three sentences are fine for everyday conversation. Any native (American) speaker would easily understand the meaning of any/all of your sentences. Hope that helps!