According to the MTA:

F Coney Island-bound trains run via the from Roosevelt Av to 47-50 Sts

Weekends, 11:15 PM Fri to 5 AM Mon, until Oct 27

Trains run express from Roosevelt Av to Queens Plaza.

No Coney Island-bound service at 21 St-Queensbridge, Roosevelt Island, Lexington Av/63 St and 57 St.

We may learn more about the timetable for ending the Roosevelt Island Weekend F train subway service disruptions during October 22 CB 8 Roosevelt Island/ Transportation Committee joint meeting. Among the items on the agenda is:

… Update on weekend subway diversions…

at:

Manhattan Park Community Room
4 River Road
Roosevelt Island, NY
Wednesday, October 22, 2014
6:30PM

as well as presentation on the NYC Department of City Planning Western Queens Transportation Study concerning Roosevelt Island.