if he's on active duty

[navi tasan]

1) The contract includes a clause about his death if he's on active duty,
2) The contract includes a clause about his death if on active duty.
3) The contract includes a clause about his death while he's on active duty,
4) The contract includes a clause about his death while on active duty.

Which of the above sentences are grammatical and meaningful?
Which are natural?

 

[5jj]

All of them.

 

[5jj]

I'd use (2 or (4, but I'd probably omit if/while.

 

[Annabel Lee]

I think the sentences would work much better if "his" were omitted:

5) The contract includes a clause about death on active duty.​

​

When he signs the contract, it will be understood that the clause would apply to him if he should die on active duty.