Get an attorney? Really? Wow talk about a super conservative and expensive answer to a very simple question.
Brad, I AM a landlord in PA. Just start with the simple stuff - READ the current lease. This will spell out CLEARLY if you're current presence there is "allowed" or not. If there is no clause that directly prohibits it, then that's ok. In any case it is not YOU that is potentially violating whatever lease is in place right now - that would be your roommate, not you.
Anyway, bottom line is if you two have been good tenants (clean, quiet, paying on time), it is pretty likely that the landlord would love to get your call and simply keep you in place. Sure, you may be required to fill out an application and credit check but that's no big deal.
What do YOU want? Do you want to stay, if the price is right? There may be some really good opportunities available to you with vacancies in your area that you may not be aware of ... So if moving wouldn't be too horrible, then think about your next options. Check out Craigslist to see what's listed there. Also you can post your OWN AD so that prospective landlords can find you (we do that).