if you do some research on the topic, you will find that long leave is not a issue. This doesn't mean that you will not be taken aside from the line for questioning. It is upto you to prove that you are still employed by the company when u come back. This can be done by letter of employment. 

For your next question, you will need to be in H1 till you convert or apply for F1 via school.

Pls consult the lawyer or the school's internation advisor..