If you do not pass your CPL AND your IR wihin 36 months of the pass date of your last written exam you lose your ATPL credits.
If you have got your CPL issued within that 36 months, but not your IR, you keep your CPL, but in order to undertake an IR you would have to, as a minimum, do the 7 IR theoretical exams.
However, this does not give you a frozen ATPL so you will not be able to fly for the airlines. To do that you would need to retake all 14 ATPL exams.
Linda Mollison