Is plastic surgery the only solution for a big pannus?

I'm afraid so: Once the skin has been stretched beyond its capacity to retract (for example after massive weight gain and then loss), it will not go away by itself. Sometimes removal of a pannus is covered by health insurance. See a board-certified plastic surgeon to discuss all of your options.

Big pannus: First, diet and exercise should be optimized to reduce the size of the pannus as much as possible. Any hernias should be addressed. Liposuction may be performed to help reduce the volume of fat in the pannus. While there are non-invasive fat reduction technologies available, a large pannus may only be completely removed with surgery.

Probably: If weight loss doesn't result in loss of the pannus, surgical excision likely is the best option.