It can feel like the end of the world!
You need to hire good professionals.
Your lawyer and your realtor know how to deal with these situations.
If the delay is NOT your fault, then don’t worry. All associated costs will be borne by the other party.
Recently I had a home close about a week past the original closing.
My sellers incurred extra mortgage costs, property taxes, legal expenses, and more. This was mitigated by an agreed-upon fee from the buyer at the time of closing a week later.
It's always best to try and work out a delayed closing.