Quote from Martin Schweiger on October 9, 2020, 5:04 pm

You can file a petition to revive a PCT application for missing the national stage deadline.

Requirements:

1. Petition for Revival of an International Application for Patent Designating the U.S. Abandoned Unintentionally Under 37 CFR 1.137(b);
2. Petition fee 37 CFR 1.17(m) ($1,000 for small entity);
3. Proper reply (i.e., the US national application and all necessary documents and fees associated with entering the US national phase);
4. Filing a statement that the delay was unintentional (contained in Form PTO/SB64/PCT): “The entire delay in filing the required reply from the due date for the required reply until the filing of a grantable petition under 37 CFR 1.137(b) was unintentional.”