I own Mikimoto pearls purchased in the 90's. You are correct, the clasp looks like a figure 8 with a small pearl in the center.
Sterling Silver Mikimoto Clasps by: Beth
I"m sorry to hear about your necklace. The Mikimoto signature has not changed. "M" inside a shell.
I have an early 1930's Mikimoto brooch and earring set in Silver. It is over 80 years old and it is marked "S" inside a square for Sterling Silver. It also has the "M" inside a clam shell.
The earrings are also marked "M" inside a shell and "S" inside a square for Sterling.
I'm not sure about the necklaces, but i would imagine, Mikimoto being Mikimoto he wouldn't have just stopped at one or two necklace clasp styles.
I hope you find out if these pearls are yours and returned to the rightful owner.
