Exchange of experience in rescheduling appointments

what does completion mean? Have you defined that? Are you building turnkey? Do you have a construction schedule and a payment plan?

Turnkey, yes. There is no construction schedule. And the payment plan is only defined to the extent that there are invoices in stages, so for example, when the foundation slab is completed, a payment becomes due, and so on.

You can't do anything at the moment. Breach of contract is out of the question. Whether you can get other craftsmen at all is also uncertain. Just plan for 3 or 6 months longer. We all do that, whether in house construction, school, visits to relatives, or vacations. Address the problem reasonably on the construction site. Don't be unreasonable.