If I reactivate my Facebook account after leaving it deactivated for several months, will my posts from several months ago show up on everyone's timeline immediately after I reactivate?
Yup, if you reactivate your account. All post, comments, information will remain exactly the same as it is when you deactivated your account. Including likes and comments!
I have never deactivated my account so here are the sources:(I'm not very sure about this)