Hi there!
I have exactly the same issue! Welcome aboard! ;D I consulted a lawyer on this, who explained that I cannot work without a valid work permit (WP). He sugested for my employer to get a new Labour Market Opinion (LMO) and then for me to apply for new WP 30 - 45 days prior to current WP expires. Mine expires end of June, but I'll not get my Open Work Permit until end of July, and that is best case scenario. So, I'll ask my emploer either he's willing to obtain new LMO and in case he does not - sucks to be me, I'll be staying as a visitor until I have my OWP and then will look for another job.
Please let me know if you'll find out about any other option.
Good luck!