Not all FF points expire in 3-4 years, its actually closer to 5 for SQ, the initial 3 years can be extended 6 months, the restriction is that they must be booked (they are not required to be flown) in that period, you can then book 11 months out and my experience is that this can be changed almost up to the flight date beyond the 11 months but YMMV.
Have you considered moving what you will use in this period to SQ/CX, move some more to programs without that restriction to at least get some of the benefit before they devalue?