It used to be the following case under JAR when your ATPL credits expired after 3 years:
No CPL or IR = all 14 credits lost
CPL held, no IR = 13 credits lost (VFR comms granted)
CPL and IR = ATPL credits remain valid for 7 years from your last IR renewal
If you held a CPL, you could however just do the IR exams to then gain a CPL/IR however its NOT a FzATPL so no multi crew types allowed. You would still need to redo the CPL exams (minus VFR comms) to get a Full FzATPL.
Crazy crazy stuff but I've no idea if its changed since EASA....would be interested to hear...