Antenna can grow back. Heck if an Apple Snail loses an eye it regenerates another! Look for damage to the foot. From what you have described the snail is just fine except for a shortened antennae.

Do mystery snail feelers grow back?

Mystery snails (Family Ampullariidae) are aquatic prosobranchs which possess structurally complex eyes at the tip of a cephalic eyestalk. ... These snails possess the ability to regenerate the eye completely after amputation through the mid-eyestalk.

Can a snail survive on its back?

Some snails can flip themselves over like acrobats, but others may need a hand if they get stuck. ... Turbo Snails (Turbo sp.): While some Turbo's can flip themselves over, most struggle. These snails end up on their backs often since they tend to be glass-climbers and fall off frequently if startled.