somewhat

My offer is yearly renewable. If you have 2 years it will be fine from my point of view. NIW does not require employer support. You don't have to have permanent position. But as I suggested in my previous e-mail you'd better provide rec. letter indicating that your employement will be long term. The offer or contract are not nessosory to provide.
If you provide offer letter I think that you still can get approved but maybe you will receive REF to prove that you are still work.