Be very careful about how you deal with this. Decommissioning a pool is not a simple job, and removing an in-ground pool usually requires an engineer to sign off on the plan and you end up with a very big headache if you try to pull off a DIY hack job.
You should also not leave the pool empty. Frost in the winter, and the water table otherwise, produce buoyancy forces that can cause the pool to lift out of the ground and make an even bigger mess for you to deal with. A pool is meant to be underwater and its surfaces, finish, and structure will continue to deteriorate if it is not maintained and operated. The costs to fix it will just get bigger. If you're going to cover it, you need to either keep water in it and maintain it or you need to permanently decommission the pool and fill it or remove it.
A complete removal is the most expensive option, but if you do a complete removal properly, with an engineered plan, you gain two things :
- If you ever list the house for sale you would not need to disclose that a pool used to be there. The land where the pool used to be will have been properly cleared of old concrete and backfilled with suitable materials for support and drainage such that a future structure can be safely built on top of where the pool once stood. It will be like the pool never existed.
- If you yourself want to build a structure in the space reclaimed by the pool, you can do so legally and with confidence that the ground under your new structure will not let you (and, by extension, itself) down.
The alternative is to simply fill the pool. This requires at least breaking up or drilling the bottom of the pool to allow drainage and filling it with backfill material. Even in this case you will likely require a permit from your city to do this work. A pool filled in such a manner must be disclosed when selling the house and it will negatively affect the value of the house. If you bury a pool improperly and hide that information when selling you open yourself up to rather unpleasant liability (even for yourself if you don't sell and the rotting, badly buried pool causes erosion that, say, threatens the foundation of your home - your insurers will not forgive your errors). In any case, there will be local regulations that you must follow when filling the pool so be certain that you understand your responsibilities before starting.
The best option here is to consult professionals.