Ye don't take account the appreciated asset. In 2021, house prices are forecasted to see 3%to 5% across the board. Some places even higher.
If his 160000 house rises three percent only it's worth 164800 next year. He needs to take this potential appreciation into consideration in his decision. Yes prices can go down, but that's not what's forecast.
While if you decide to keep the original property the capital appreciation or depreciation is likely to be the biggest element of the actual outcome in the years to come. Strangely that is mostly irrelevant to the decision
First of all if the rental return does not work then you should not have a rental property. In this case the rental return does work. I see Zenith63's view that there is a lot of work for little reward, but equally I could ask where else can you get 3% return on someone elses money.
Think about that for a moment, the return on the rental here is on the banks money, not on the OPs money. The OP does not have the alternative of investing €160k in shares because he does not have €160k to invest and the bank wouldn't loan it to him. But for this specific purpose he can borrow 160k and invest it to get a return after tax and after interest. Thats is an oportunity that he may never have again.
Back to the question of how to value the possibilities of the change in capital value. The upside/downside potential is not symmetric for the OP. No matter what happens to the capital value, the OP has to repay the bank €160k, he can cashflow that from the rental income over 20 years or whatever (if an investor cannot repay cap and int over a mortgage term, then its a bad investment) . When he sells the property he will have the price give or take CGT. If that is €150k he will probably feel he has lost out, but in reality his costs were just higher over the term, €500 pa in the case of 10k over 20 years.
The final sale price is irrelevant to the decision, (especially because you have no way to know what it will be) if property increases significantly great (well great for the OP whatever about society), but it would be foolish to count on that when deciding to invest.