Can spleen get raptured months after mono infection?

Unlikely : In medicine we learn not to say always or never. That said, the spleen as an active organ in the immune response to mono can swell within its capsule & rupture from a significant fall or contact (off a horse, football tackle, wreck). For many it never swells much and or the swelling subsides within 3-4 weeks. After swelling subsides it has the same baseline rupture risk it always has.