The you and me pointer will automatically be set to NULL when the corresponding entity gets removed, so you don't need to take extra care about that.

When using custom pointers there is no way to check if the entity exists. The pointer just contains an address, regardless if the entity exists or has already been destroyed. Accessing such a pointer will always result in a crash or worse - overwriting random memory and a crash later on. ^^

If you don't want to use the me or you pointer you better switch to handles. You can get an entities handle by calling the handle(ENTITY*) function and can check if the enity still exists by calling ptr_for_handle(fixed). This function will return NULL if there is no entity with the given handle.