@A G. As long as your neighbor (the owner) didn't take advantage of the tenant in any way, and as long as the previous property manager didn't take advantage of the tenant, I don't see how changing a property manager or consultant removes tenant's responsibility to pay rent. Now if tenant was taken advantage of or harassed by any of the parties involved then that is a different story.
As far as the part of the lease that you posted "If Tenant vacates prior to the expiration of the Lease term, the entire Security Deposit shall be forfeited";
Based on Oregon landlord/tenant law which the Washington law is similar, a rental agreement/lease can't stipulate that a tenant forfeits all of his security deposit.
Your lease can stipulate that lessor/landlord will claim and retain part or all of the security deposit necessary to cover lessor's damages due to early termination. So, that may be why your tenant quoted the "severability clause" to let you know that the section of the lease stating that he will forfeit his security deposit is invalid per the law.
But what your tenant failed to realize is that the same law states that he is liable for rent for the duration of the lease or until lessor re-rents the property whichever occurs first.
I always advise landlords or property managers to read and master the entire landlord/tenant laws in their area or hire an attorney otherwise the pro tenants will take them for a ride. Again, good luck to you and your friend.