It is very unfortunate when a roommate abandons the lease and just leaves you fully responsible for finding a subletter. In this case, you can usually speak to a landlords and explain the situation. Unfortunately, if you and your roommate both signed the lease, it makes you both legally responsible for it. So, if you're continuing to stay in the lease until end of its term, we do recommend that you find a substitute subletter to avoid paying for the entire lease all on your own.
Can you sue your roommate for breaking the lease?
It's easier said than done. You can try to do that, but it will be a waste of time. You have to still continue paying your landlord, based on the terms of your lease. Filing a suit against your roommate who failed to pay on their terms, will eat up your expenses and take up your time. It's always best to find a replacement tenant for your lease and get this all past you.