Comcast CEO Brian Roberts said some guests may not return to theme parks until a COVID-19 vaccine is available.
"SeaWorld has determined that it must transition certain park and corporate personnel from a furloughed status to a permanent layoff," the company said in a statement.
Also delayed will be Emperor, Pantheon and Ice Breaker.
Busch Gardens Williamsburg is one of three SeaWorld-owned parks that remain closed.
Two Epcot area resorts are now set to remain closed until further notice.
Disneyland unions wrote to California Gov. Gavin Newsom, saying they're not convinced the resort can be operated safely for a July 17 reopening.
This is one of dozens of liens filed against SeaWorld by vendors and contractors for unpaid work.
Busch Gardens Tampa Bay's reopening plan doesn't include a proposed date for welcoming back guests.
Serge Rivera is the company's fourth CEO in the past six years. Like his predecessor, he's leaving over disagreements with the SeaWorld board's involvement in company decisions.