You are on a tight schedule. A radon test usually takes two days of testing before an analysis can be made. You need the new system installed and running prior to testing. Talk to your attorney and see if funds can be withheld from the seller in escrow to ensure you no longer have a radon issue. And talk to the bank about test results. You may have to do a dry closing ( closing without funds transfered or keys delivered) until this can be resolved.