This is not as unusual as you may think. Examples abound in such mega projects where a major civil works contractor default and another one walks in to pick up

This is not as unusual as you may think. Examples abound in such mega projects where a major civil works contractor default and another one walks in to pick up the mess. In addition, the path of the tunnel will be decided in details and subjected to various authorizations so mess will be limited. Delays will occur but, regardless what Elon thinks, there are plenty of reaaaaally good tunnel makers on this planet that will happily come and finish the job.