From the airlines point of view, as an employed FI, you are in current practice, and hopefully also teaching the IMC rating or IR.
You will quickly go "off the boil" having completed your training unless you keep flying.
The FI route can be a very useful in improving your skills and developing airmanship.
You are also accumulating hours to unfreeze that ATPL.
Completing the CPL/IR training, and then virtually stopping flying, apart from the yearly IR renewal, is not an option.
You will more than likely be assessed as a training risk if you have not flown in the last six months or so.
Why take that risk when you are invited for that all important interview. Bottom line - keep current.