1. as long as the lien was not file, you can close.
2. get an attorney now, and send him a warning letter, if you can not close on time, you will counter sue him so he will be responsible for all your lost if the court determent later the claim is false.
3. if he file, you can still close but usually you have to escrow 150% of the claim amount till the lien gets settle.
hope this help. I am a builder.