This is the reason one should know future roomies VERY well, esp before signing a lease! A month-to-month tenancy would have been better ...remember that in the future.
One thing on your side is that roomies have a duty to try to replace you and mitigate damages if you break the lease and leave, so you should not be obligated for the entire rest of lease. They can't just sit back and say you must pay anyway.
If they sue you, they MUST prove they did everything they could to get a new roommate. You would be responsible for any rent before new roomie. OR you could get a roommate to replace you.
But signing a lease with anyone essentially puts you in bed with them financially and there are no easy outs. Good luck.