They immediately fall out of status because F-1 requires continuous enrollment in a SEVP-approved institution.

USCIS may issue a notice of unlawful presence, which can lead to bars on reentry if they stay too long.

They could try to transfer to another school or apply for a change of status (e.g., to B-2 visitor) before accumulating unlawful presence.

If caught out of status, they could face deportation proceedings.