Highly unlikely, except perhaps in Jake Davis's wet dreams.
Remember that an actual hack requires a both a great deal of skill and great deal of luck, especially when reasonably secure installations (FB obviously qualifying as "reasonably secure") are the target. If this group had the skill required, they would know enough not to be counting on getting lucky. Thus, either they already have knowledge of some vulnerability, or they're not going to find one. The former is highly unlikely - if they had that knowledge, it would require a great deal of stupidity to count on FB not discovering it for nearly three months.
Remember that an actual hack requires a both a great deal of skill and great deal of luck, especially when reasonably secure installations (FB obviously qualifying as "reasonably secure") are the target. If this group had the skill required, they would know enough not to be counting on getting lucky. Thus, either they already have knowledge of some vulnerability, or they're not going to find one. The former is highly unlikely - if they had that knowledge, it would require a great deal of stupidity to count on FB not discovering it for nearly three months.