The tax treatment of debt write off is a bit strange.
In relation to interest if it is not paid then it can be claimed as a deduction, if it is claimed and subsequently written off it should be include as income.
In relation to the capital element of a loan written off, the write off is not taxable in itself but what the write off does it reduces the base cost of the asset where there is a capital loss.
So Bob paid €1m for the asset and gets a write down of €200k. Bobs base cost for computing a CGT loss is €800k rather then €1m.