@tim I agree with @artyeasel. Impairment’s effects on net income, disregarding time effects should net out. But I’m not sure if CFAI will ever ask a question like that!
ROA and ROE will increase going forward (as your assets have decreased) as well.
To answer a part of your question – impairment is effectively immediate ‘forced depreciation’ of a particular asset. So yes, the net income differences does balance out assuming no discounting.